Summary

How do you choose your wheel offset? Blindly fitting a set of wheels to your car just because they sit inside the guards and look good could lead to serious handling compromises. At best you might have to drive slower on track and look like a bad driver, at worst you could get caught out by unexpectedly poor handling characteristics in dramatic fashion, causing serious damage to your car, or worse, someone else's. In this webinar, you will learn how wheel offset affects track width and scrub radius, as well as the lead-on effects these have on our handling performance.

00:00 Hey team, Connor here from HPA and welcome to another one of our webinars.
00:03 This week we're going to be talking about wheel offset and the effect that this has on handling.
00:08 So, we're going to get started by covering exactly what wheel offset is, so we're all on the same page, and then we're going to talk about the effect that this has on track width and scrub radius, and then the lead-on effects that this would have on our handling.
00:23 So, let's get started by just talking about what wheel offset is.
00:27 And if we jump onto my computer screen here, I just have a CAD model open in Fusion 360, which is going to help us show exactly what wheel offset is.
00:41 So, in this case, this is a wheel without the center, three-piece wheel without the center, but we've got the hub here and the brake package as well.
00:50 So, what the wheel offset is, is it's the distance from the mounting surface of the wheel that mounts to the hub here to the center line of the wheel.
01:00 So, if I looked at the top view of this and we made an imaginary center line through the wheel, it would be the distance that that is offset in that case.
01:09 So, if I just chuck a section through here, so we'll just split that in half, what I'm going to do is just create a sketch on that top plane, and we'll be able to measure here what the offset I have of this CAD model is.
01:24 So, what I'm going to do is just start by projecting some lines of the bead seat.
01:30 So, that's where the bead of the wheel rests on the rim, the bead of the tire, sorry.
01:38 And then what I can do is just draw a line between the center points of those through our wheel.
01:45 And then I'm also just going to project that face onto our sketch, and then drop a point on the center there.
01:59 So, if I quickly hide everything, look at the top view, we can see that this is the center line of our wheel here, and this is the mounting face of the wheel, or the mounting face of the hub that the wheel would be on that.
02:16 And then I can measure between those two, and I have 15 millimeters.
02:23 So, in this case, where the center line of the wheel is 15 millimeters outboard, so further out than the mounting face, that would be what we call negative offset.
02:39 So, this would be negative 15 millimeters offset.
02:42 If that center line was on the mounting face here, that would be zero offset.
02:48 And if it was inboard in this case, then we would have what's called positive offset.
02:54 So, when we have more positive offset, that brings the wheel inwards.
03:00 So, if I just jump back here, and go back to about here, that would be more positive offset.
03:08 So, the wheel is more under the car if you think the hub is going to stay in the same position.
03:14 More positive offset like this is going to move the wheel inboard.
03:19 And then if we come back out, more negative offset is going to move the wheel outboard.
03:24 So, again, more positive offset tucks that wheel in under the guard of the vehicle, and more positive offset is going to poke it out a little bit more, fill out the guards, or if you go too far, poke outside the guards as well.
03:39 So, hopefully that explains what the offset of the wheel is.
03:43 And that's a little bit different from backspacing that a lot of people like to mention.
03:49 And that is where the distance between that mounting surface and then the back of the wheel here.
03:55 So, if you have more backspacing, you generally have a more positive offset.
04:00 Or it really just that the wheel width also factors into that.
04:05 So, the offset has nothing to do with the wheel width.
04:08 The width can change and the offset can stay the same, or the offset can change and the wheel width can stay the same.
04:18 Those two aren't linked together where the backspacing is linked to the wheel width and the offset to some degree.
04:25 So, what we're going to do from here is just jump on to discuss the effect that this has on some of our handling characteristics.
04:36 And first of all, it really comes down to the impact that the wheel offset has on our track width and then also our scrub radius.
04:45 And those are the main two lead-on effects it has that then influence our handling.
04:52 So, before we get into it, I just want to make a note that if you have any questions I'll try to, that are relevant to today's discussion, I'll try to get to those at the end and do my best to answer them.
05:06 And then I just want to make the comment that all the effects that we talk about here are assuming that everything else is equal.
05:14 If we're saying this change makes this effect, it's assuming that everything else is the same.
05:20 Because otherwise it just gets too complicated and easy to kind of argue with those facts.
05:26 And often when we are making these changes, other things change as well.
05:30 So, that all else equal kind of goes out the window.
05:33 But we kind of need to set that in stone so we can make these comparisons.
05:38 So, from here, what we're going to talk about first is the track width.
05:43 So, I've got this image up on my screen here.
05:46 And this is actually taken from our wheel alignment course.
05:53 And this shows the wheel base and the wheel track on the front axle here and the rear axle of the vehicle as well.
06:00 So, looking at the bird's eye view down on the vehicle.
06:04 So, the wheel track is the distance between the center lines of the wheels on the same axle.
06:11 So, in this case, we're looking at the front axle.
06:13 Now, the center lines, that's the track width.
06:16 It's not to the outside of the wheels or the inside of the wheels.
06:19 It's the center line.
06:21 So, we can have a different wheel track width on the front axle to the rear axle.
06:28 In fact, that's very common.
06:30 We often see, especially in rear wheel drive cars or mid-engine cars as well, a wider track on the rear of the vehicle.
06:38 And the reason that we talk about the track width and compare that to the wheel offset is the wheel offset has a direct impact on the wheel track.
06:51 So, yeah, the wheel offset has a direct impact on the wheel track.
06:55 So, if you think and look at this, we could change the width of the wheel.
06:59 But if the offset is still the same, the center line is still going to be in the same place.
07:04 So, the wheel track is going to stay the same.
07:07 But if we make any change to the wheel offset, if we make it more positive, that's going to shift the center line inboard and narrow the track.
07:17 And if we make it more negative, that's going to shift the wheel center line outwards here, and that's going to widen the track.
07:26 So, again, lower offset widens the track, higher offset narrows the track up.
07:33 So, from here, what we're going to talk about is the influence that the track width has on the handling.
07:42 Now, we know what difference the offset makes to that track width.
07:46 So, if we just jump over here, I have this equation up on my screen, again, taken out of one of our courses.
07:53 I think this is the suspension tuning and optimization course.
07:56 And this is saying that the lateral load transfer, which is how much load is transferred between each side of the vehicle as we go around a corner, for example.
08:07 And that's equal to the vehicle mass multiplied by the center of gravity height, multiplied by the cornering force, divided by the track width.
08:17 So, basically what we're trying to do here is we're trying to reduce the lateral load transfer.
08:23 And if we can do that, then that basically increases the grip due to other things that we're not going to get into too much here because it's kind of overcomplicating the point around tire load sensitivity and things like that.
08:36 But generally, we're trying to reduce the lateral load transfer.
08:39 And we can see from this equation, if we increase the track width here, then we're going to reduce that lateral load transfer.
08:48 So, making that track wider gives a wider base, and that means that the lateral load transfer is reduced.
08:54 So, we can clearly say that if we increase the offset of the wheels, sorry, decrease the offset of the wheels, we get a wider track width, and that's going to reduce the lateral load transfer.
09:05 So, we can see straight away that changing the offset of our wheels has a direct impact on lateral load transfer.
09:14 The other thing that we want to consider, sorry, I will just make the point there, all else equal, because there's a lot more that goes into lateral load transfer than this equation here.
09:24 This is a very simplified view of it, not including things like the unsprung mass load transfer or geometric load transfer, and the difference between that and suspended load transfer.
09:38 So, realize that this is just a simplified view of it, but the track width does factor straight into it.
09:44 Okay, so the other thing that we want to consider here is the wheel track to the wheel base ratio.
09:54 So, there's a lot that goes into this, and it depends on the design of the vehicle.
09:59 For example, a Formula 1 car is a case where the wheel base is very long compared to the wheel track, and then we have shorter vehicles like the HPA CRX, for example, where we have quite a wide track width and a very short wheel base.
10:17 But what we're considering here is the difference that it makes if we keep the same wheel base and we widen the track.
10:24 We are making a change to one relative to the other, so we're changing that ratio.
10:29 Realistically, though, the changes to this made by the offset of the wheel leads to relatively small changes, unless we're talking about something crazy like if we look at a RWB Porsche, for example, where they widen it a crazy amount and maybe by 10 inches or something with massively low offset wheels in the rear, then in that case, they are changing that ratio significantly.
10:59 Basically, a wider track to wheel base ratio does lead to more grip, all else equal again, but it becomes more difficult to kind of manage that grip as we get closer to the limit.
11:15 So, a very short, but very wide car, or if we start with a very short car and then we increase the width, it'll probably have more grip, but once we get to that point of more grip where we're reaching the limit and it's starting to break away, it'll probably break away at a lot higher rate and be a little bit harder to manage than before.
11:36 Again, though, relatively small changes made by the wheel offset here, all things kind of equal.
11:45 So, the other thing I want to talk about here is relative changes between the wheel track, the track width from the front axle to the rear axle, and this is where the offset of the wheel makes a little bit more difference.
11:59 So, like I said before, changing the wheel base changes the lateral load transfer and what we have is lateral load transfer distribution between the front axle and the rear axle.
12:13 So, basically what that means is a certain amount of our load is transferred on the front axle compared to the rear and that ends up coming down to the balance of the vehicle.
12:24 So, if we have a lateral load transfer distribution more towards the rear of the vehicle, so we transfer more load on the rear, that'll tend towards a more oversteery setup because we'll be transferring more load on the back and that reduces grip.
12:40 So, if we're reducing grip on the rear, that'll tend towards oversteer and the same, the opposite is also true where if we're transferring more load on the front axle, that will tend towards a more understeery setup.
12:54 So, if we're changing the offset, for example, at the rear of the vehicle and we are, for example, going with a lower offset wheel, so we're spacing the wheels out wider, we have a wider track and then we are decreasing the lateral load transfer from that equation that we were looking at before here.
13:16 So, we're going to basically increase the grip at the back relative to the front and then that means that we're going to tend towards a more understeery setup.
13:27 That doesn't mean the car's going to understeer, because it might have been so far in the oversteer direction that we're just shifting the needle a little bit closer to understeer or a more balanced setup or maybe it's already understeering a lot and then we go and put really low offset or wide track rear wheels on it and then we make the situation worse, which is basically, and those little changes that we make with the offset are going to have a more significant impact on this as well so it's something that we do need to be aware of, but it can also be used as a tuning tool as well.
14:01 It's quite easy to go and make a change like that compared to maybe changing to, for example, a stiffer sway bar in the back to make that balance change or a softer sway bar to make that same balance change rather.
14:18 So, yeah, it can be a tuning tool or a blind change to the wheel offset could be potentially making matters worse for yourself.
14:28 So, that's the wheel track width, the wheel offsets effect on track width and that effect on handling covered, so from there we're just going to jump onto scrub radius.
14:41 So, this is a short video here taken again from I think our wheel alignment course.
14:50 So, all this is showing here is for a McPherson strut setup, we have the kingpin inclination or steering axis inclination angle here shown in red, so for a McPherson strut that's from that centre of our strut top bearing through the outer ball joint for the lower control arm onto the upright there and that goes through and extends out to ground level at the contact patch there and then that blue line being drawn down there now is the centre line for the tyre.
15:24 So, this is looking straight at the front of the vehicle, you haven't seen that faded out shoulder the front of a GT86 there and the distance between those being our scrub radius and if we just drag this on a little bit here, we'll see that if we reduce the offset of the wheel, the wheel will move out wider there, poke outwards from the car and then that's going to increase that scrub radius, the distance between those two points there.
15:54 Cool, so that's what our scrub radius is.
16:01 I just want to show as well, I don't have quite as nice of an image here to use , but this is a McPherson strut and we would have the kingpin inclination angle between our top ball joint on the upright here and our lower ball joint, we don't use the strut top in this case because this is the steering axis, so as we turn the wheel this is the point, the axis that it rotates about.
16:29 So, I think I can draw a line between these, so it would come down like that, meet the ground and then if we also drew a centre line down through the wheel, sorry that's not very straight, then we get to the centre of the contact patch there and our scrub radius would be like that rather than drawing it from the centre point of the strut top.
16:57 This is the steering axis for a double wishbone setup, so just a little bit different to the McPherson strut, but we basically end up in the same position and it's describing the same thing.
17:09 So, it's the point around, the difference between the point the tyre rotates around with steering to the centre line of the wheel.
17:22 You might realise that if you're kind of familiar with this stuff, if we looked at this from the side view, the kingpin inclination would be replaced with our caster angle and then the difference from our centre of our contact patch would become, that difference there would become our caster trail or mechanical trail.
17:45 We're just not covering this because the wheel offset doesn't have a direct impact on this.
17:53 So, we're focusing on if we make changes to our wheels here, what difference will it make to handling and changing the wheel doesn't change that, that's changed just by the suspension geometry.
18:06 And on that note you see, so if we had a look at this before and we make a change to our wheel, we can change the scrub radius , but we could also change the scrub radius by changing the angle of this axis here.
18:19 So, if we added, bent this over for more negative camber, that would actually move this point out and in this case it would reduce that.
18:28 So, I just want to make the note though that this scrub radius, if these two points were straight on each other, then that would be zero scrub radius because there would be no radius there.
18:41 If this point here was further outwards, that would be what we call negative scrub radius and as it's showing at the moment that would be positive scrub radius in this case.
18:53 So, it's not quite as simple in saying that reducing the offset of the wheel, moving it out further is going to make the scrub radius higher, I guess.
19:11 It's going to make it more positive, because if we're starting with a scrub radius that is negative, so this red line is actually coming out here, and we're moving the offset lower, then moving the wheel outboard more, we're actually going to get a smaller scrub radius.
19:32 So, it just depends on that starting position that you're in.
19:35 Yeah, it's not as simple as saying that a lower offset equals more scrub radius.
19:42 It could actually be reducing it if you're moving towards zero.
19:46 Okay, the scrub radius, so basically if we just imagine if we looked at a top view of this tyre, where the centre point, where the steering axis meets the ground is where the tyre is being scrubbed around if that contact patch is off there.
20:05 If the centre of the contact patch is lying on where that steering axis intercepts the ground, then the tyre will pivot about that point as well.
20:16 But we'll have a look at a few more images in just a second that should explain that a little bit better.
20:22 But basically the scrub radius here becomes the lever arm on the steering.
20:28 So, if we think that all the forces are going through the centre of the contact patch here, then this here, if we have a force at a distance from the point of rotation, then we have that lever arm or a moment created about that centre of rotation there.
20:48 So, it would be easy to assume in saying that a larger lever arm is going to pull on the steering wheel more, but that's not always the case.
20:57 So, we're just going to jump over to another image here.
21:01 We'll jump back to this one and we're just going to use this image here to kind of show that.
21:06 So, we're going to zoom in on this image in this case and just use this as a bit of a diagram.
21:12 So, I'm going to draw on this, so just bear with me if my drawing's not very accurate.
21:19 So, there's a few different directions in , which the forces could be applied to the contact patch, but they're always going to be applied, well, not always, but they're always going to be applied, not always, but the external forces from the tyres are going to be applied through the centre of the contact patch.
21:37 So, if we think about a negative scrub radius, then we're going to have, just draw some points here, the centre of the contact patch is about here.
21:52 Oh, it's not wanting to do it.
21:54 Bear with me there.
21:55 So, the centre of the contact patch is here, shown in green, and the steering axis inclination, where that goes through the ground, is going to be out here.
22:09 Sorry, negative scrub radius here, it's going to be out here.
22:12 So, this is our scrub radius in this case.
22:16 If we have a force through the tyre, show this in blue, from braking, it's going to be pulling back on the tyre like this.
22:28 So, this is our fixed point here that it rotates about, and it's pulling back on the tyre like this.
22:34 So, we're going to have a moment pulling around, and that's going to be trying to tow the wheel in, so force the wheel inwards here.
22:45 So, if we have that on each wheel, they're going to basically point in and towards the centreline of the vehicle, also called toe in.
22:55 If we change things a little bit here, and we move the steering axis inclination into here, so we have a positive scrub radius in this case, then we have a slightly different story, so if we have this force acting on the contact patch here, and the point of rotation is fixed here, then this is going to do this with a moment, and that's going to be trying to tow the wheel outwards.
23:37 So, basically, under braking force, if we have a negative scrub radius, it's going to tow in, and what that tow in does is it makes the vehicle more stable, so under the braking, when we're on the brakes, that tow in makes the vehicle more stable, but if we had a positive scrub radius, like what's shown here, it's going to tow outwards, and that's going to basically make the vehicle less stable, and it'll be more prone to darting off, I guess you'd say, in different angles.
24:08 This negative scrub radius situation, not shown here, I'll just go back and show you that, if we move that up, and that toeing in, that also helps if we have a split mu surface, what we'd call it, so basically if one of the front wheels, , which do the majority of the braking, drop onto something like ice, or off the side of the track, for example, the wheel that has the traction is going to have more force pulling it and trying to rotate the vehicle, so spin it one direction, , but that torque is actually going to pull it inwards, and that is going to counter that effect, so this actually, this negative scrub radius situation here ends up giving us more stability in a situation where we drop one wheel off the track, and that's going to counter that effect.
25:02 So, if we drop one wheel off the track and are hitting the brakes, or we're trying to brake the car on ice, patches of ice where one wheel is on the ice and the other one is not, for example, so that negative scrub radius helps a lot there as well.
25:16 The magnitudes and effect of this tow in though, and tow out is really going to depend on the compliance in the suspension, so if we talk about an older vehicle with really soft rubber bushings, for example, there's going to be more compliance in the suspension and it's going to be more prone to the alignment moving, so the tow in will be more excessive than, for example, if we're talking about a race car that has solid bearings and everything's very stiff, it's not going to be so much of the case.
25:53 The same kind of idea here applies if we're talking about bumps on the road or hitting a pothole or something like that, the forces on the tyre or the wheel are going to be similar to the braking forces here, pulling that on the wheel, and they're going to result in the same thing.
26:09 So, basically that negative scrub radius is going to tow in if we hit a pothole and it's going to, basically a negative scrub radius is going to end up with more of a stable, yeah, more stability in a straight line if we're hitting bumps and the likes of that.
26:28 If we have a really high positive offset and we're driving down the road or on the track and we're hitting bumps on one wheel and we have a really big lever arm there, it's going to be pulling and toeing out that side and trying to pull the car all over the place a little bit more.
26:46 So, we'll move on a little bit from that and talk about the other direction that the force could be coming in, so that would be from the drivetrain, and here we're just going to be focusing on front wheel drive and all wheel drive because we're looking at the front axle in this case and we're talking about steering, and front wheel drive and all wheel drive are the only ones driving the front axle wheels of course.
27:08 So, in this case this force would be going in the opposite direction, so the forces on the tyre would be like that and in that case if it's rotating about this point then the inner front wheel drive, any way or all wheel drive, if we have negative scrub radius then it's going to be toe in the front wheels outwards under acceleration.
27:40 And the first thought is that might seem more unstable if we're toeing it out under acceleration, but what that does is it actually ends up counteracting some of the uneven forces from torque steer.
27:55 So, if I just zoom out a little bit and we talk about torque steer, basically what we'll have is one wheel, these are the drive forces, I'll do that again, sorry, so if this is the tyre force on this side and then we have a bit more tyre force on this side we're going to end up with torque steer, but we're also going to have the same thing here toeing this one out.
28:26 So, basically this uneven force here is going to want to drive the car around this way and that's how we get torque steer, but that uneven force there is going to end up with a bigger moment pulling this way and that's going to counteract some of that there so it actually ends up with a negative scrub radius in this case helping to reduce those torque steer characteristics in front wheel or all wheel drive cars.
28:54 If we have a positive scrub radius in that case it'll actually add to the torque steer so it can make it a lot worse.
29:02 Just on that note I talked to, I forget the guy's name, but he's got the K11 Nissan March with the SR20VT in it, races at World Time Attack, little red car and it's about 650 horsepower in a Nissan March through front wheel drive and I was talking to him and initially he was running really wide low offset front wheels on it and he actually ended up changing to narrower front wheels because he said the torque steer of the wider front wheels was just unmanageable.
29:34 So, that's a bit of a proof of that shown in action that reducing the scrub radius actually helped counteract that torque steer a little bit.
29:46 So, the other thing we need to talk about is steering effort.
29:52 So, if we're actually steering the vehicle, we would assume that having a larger scrub radius is going to make it more difficult, because that centre point of the wheel is scrubbing around the centre point of the steering as we're kind of dragging the tyre over the road surface, but it would only be dragging it over the road surface if we were locked up on the brakes and actually what happens is if we're off the brakes and the wheel is free to roll, having that distance allows the wheel to roll around the centre point of the rotation and that was really used more in older vehicles that had no power steering, they'd use a larger positive scrub radius to actually make it easier at very low speeds like parking and things like that to rotate the steering or rotate that wheel for it to roll around that centre point.
30:52 So, it's not actually going to be a case that having a zero scrub radius is going to be easy to steer when the car's sitting on the ground, although that might be the kind of common misconception there.
31:07 But all of this always changes with speed and the different setups so as we start driving the car, that changes it a lot as well.
31:15 But in general what's considered is that more scrub radius provides more feel so as we start moving, that bit of a lever arm from a positive scrub radius or having scrub radius actually provides some bit of resistance or steering feedback, so we can feel the grip of the front wheels a little bit.
31:38 So, we can see from that that there is good and bad of both situations of having negative scrub radius or positive scrub radius, both have their advantages and disadvantages, there's always compromises with these things in motorsport.
31:53 What I would say is that we just don't want to be too excessive in either situation.
32:00 So, it should be generally in all cases less than about 40 mm, unless we're talking about a certain vehicle that's maybe very old and got a very different design for example.
32:11 But generally we're going to want that to be less than 40 mm of scrub radius, positive or negative in most applications and usually we're going to be wanting to be actually under about 20 mm, we should be looking pretty good in that case.
32:27 Front wheel drive and all wheel drive vehicles, especially those with McPherson strut tend to have negative scrub radius to reduce that torque steer and double wishbone vehicles, rear wheel drive vehicles like for example that FD RX7 that we were talking about before, that would tend to have a positive scrub radius as well.
32:53 So, the other last thing I want to talk about on the topic of scrub radius is that zero scrub radius is not actually always what we're aiming for.
33:03 When I mentioned before that we're trying to keep it within a certain range and keep it relatively low, if we have zero scrub radius, what that means is that those forces about the centre point of rotation, they will reverse direction with very small changes in the steering input basically and as they're reversing back and forth, basically what that, it's called squirm essentially and what it means is that the steering feel goes very vague and wondery and it just doesn't give us a good consistent feedback, kind of feels more like noise in the steering wheel and it's just very vague and dull.
33:48 So, having a small amount of scrub radius is actually good, we just want to keep it relatively low, if that makes sense.
33:56 Again, I'm just going to, before I make a note of a few more things, I'll get to some questions after that so if you have any questions relative to today's topic, please ask them below and I'll do my best to answer them.
34:12 So, just some other notes to finish up on, the scrub radius or sorry, more specifically to today's discussion, the offset of the wheel, typically being lower and spacing the wheel out further is going to put more stress on the components, so that bigger lever arm from a larger scrub radius, a larger track width is going to increase the loads on suspension arms, ball joints, bushings and wheel bearings as well and that is going to increase the wear on them and big increases in that lever arm from the scrub radius are going to cause more compliance and that compliance is going to be more evident in cars that have softer bushings for example than something with spherical bearings.
35:03 The other thing to comment on is spacers, so spacers are essentially just the little bit of aluminium usually to space the wheel out further and what that's doing is that is essentially decreasing the wheel offset to push it out further so the effective wheel offset goes down by whatever thickness of spacer that we use.
35:26 So, if we've got a zero offset wheel, we use a 10mm spacer, now we have a negative 10mm offset wheel essentially.
35:34 These are kind of frowned upon, but in reality they're used with success in very high levels of motorsport, you'd be very surprised where they're used.
35:45 They just need to be used safely, so one of the main things around that with using spacers is ensuring that we still have sufficient thread engagement on our lug nuts for example.
35:56 If our lug nuts are quite short and we're adding a spacer in there, we're going to run out of thread engagement so if you're using wheel spacers just be sure that you still have plenty of thread engagement on the lug nuts there and in that case it's always good to use a longer motorsport style lug stud in that case.
36:21 And we just need to understand that decreasing that offset effectively is going to add more stress to components as well.
36:31 In reality for street cars that are driven a lot, that increase wear can become a real thing that you need to consider, but for race cars generally it's not so bad because the service intervals of race cars tend to be a lot sooner and we're well aware of the expenses of running them and the wear that can happen to things.
36:56 Ok, and then the last topic is on legality so for example I'll just use the case here in New Zealand.
37:04 We have laws around the maximum change in the wheel offset that we can make, so if we are looking at the standard wheel that comes on the car, we can only change it a certain percentage, the wheel offset we can only change a certain percentage from whatever that standard spec is.
37:21 We also have limits around the spacer sizes that we can use as well.
37:25 So, as always it's your responsibility to check that with your local road authorities or motorsport governing bodies before you commit to any changes.
37:34 But yeah, hopefully that's given you some insight into the possible effects of changing the offset of your wheels and something to consider if you're looking into buying some new wheels and possibly avoid making mistakes that could make handling characteristics worse or you can also if you understand that you can use it as a tuning tool to make things better so it's not always just avoiding that issue.
37:59 So, with that covered I'm just going to answer the question we've got here and then we'll move towards wrapping things up.
38:08 "How does one actually measure the scrub radius on a real car?" Is it easy to see what needs to be measured on the, it's easy to see what needs to be measured on the diagram animation, but how do you map these points out on a car in real life?".
38:26 So, it is possible to do it if you, there's a few different ways to do it.
38:33 One way that we use in the workshop or I work in CAD a lot and I model the suspension in CAD and then I take measurements from that.
38:41 Obviously, that's not taking it from real life so that's not much help to you there , but it is possible to measure out the suspension points in space on the vehicle so using something like a plumb bob for example and measuring those points down to the vehicle and understanding that drawing out a diagram in real space or in space and then taking the measurements and understanding everything from that.
39:06 There are software offerings out there available for this that you can put those measurements into to map it out and that'll usually spit out things like scrub radius for you.
39:20 A paid one that we use is Optimum G or Optimum Kinematics, but there are free ones as well.
39:27 I think Vsus is a good option, but that's just, I haven't used that much so something to potentially look at.
39:38 Taking the physical measurement off the vehicle is quite difficult , but I've seen some people do it with laser lines as well so getting the laser pointers and lining those up with the centre of the tyre and the axis and shining it onto the ground and then measuring between them, but it's a little bit more difficult to do that.
39:57 I would recommend measuring them out in space, trying to draw a diagram and then putting that into some type of suspension software usually works the best anyway and then you can often do a lot more of it once you have that in the software as well and really get a better understanding for what's going on.
40:16 Hopefully, that's helped you out a little bit there.
40:19 That's all the questions we have so I'll just wrap it up there and thanks for coming and we'll talk to you guys next week.
40:26 Cheers.