Considerations with BBKs: How Does Changing Tire Width Affect Brake Bias?

I'm planning to upgrade to a big brake kit on my Honda S2000 and have been using the brake calculator spreadsheet to help make an informed decision. My main goal with this upgrade is to reduce compliance and increase thermal capacity. However, after taking a course, I realized that I also need to consider how this mod will impact brake bias.

Since I still street-drive the car, I’m not planning to mess with the pedal box, master cylinder, ABS, or anything like that. I also don’t have a bias bar, so the changes will only involve the calipers, rotors, and pads.

From what I’ve learned, the ideal bias should match the load distribution under the target deceleration as closely as possible.

After some calculations, I estimate that a stock S2000 has about 68% front load distribution under max braking and a 64% front mechanical bias. I got the mechanical bias from the brake calculator spreadsheet, but it doesn’t account for how pressure is distributed between the front and rear brake line circuits. Unfortunately, I don’t have an easy way to measure that directly, but from experience the factory system seems to perform well under hard braking.

For my car, I’ve calculated that the front load distribution increases to 71% due to wider, stickier 200 treadwear tires. Based on this, it seems like I shouldn't adjust the bias much since the load distribution has only shifted by 3% from stock. However, I’ve noticed the calculator doesn’t account for changes in tire size.

A stock S2000 runs a staggered 215/245 (F/R) setup, but I’m running 255/255 square. With the front tires seeing a bigger increase in width compared to the rears, I’d expect the front tires to have even more capacity before locking.

Does this mean I should bias the brakes further toward the front, beyond the 3% adjustment suggested by the calculator? Or am I overthinking this?

You may be over-thinking it a little, bearing in mind the calculator is a guide dependent on information you may not have.

Increasing the tyre width 'should" give a small increase in dry grip, but whether it's significant is a different question - bearing in mind the increased width would be expected to reduce tread temperature, and that may be less than optimum, especially with "softer" tyres?

As you want to minimise the changes, as I read it, I'd look at two things - a/ the actual disc peak temperatures to confirm if more capacity is required, with b/ looking at the OEM pads and replacement options. Bearing in mind the car has quite big brakes as stock, and the OEM pads are usually a little biased towards cold performance (including sub-zero weather), wear, etc, you may find you can get the braking performance and balance you want from carefully selecting the right pad combination. I have NO recommendations, but there are some good guides available on-line, like this one for the Lotus - https://wiki.seloc.org/a/Brake_pads - that might give some food for thought.

Something else to bear in mind is that brake upgrades usually require a wheel change to a larger diameter, which is an additional expense and may carry other disadvantages

Thanks for the feedback

My understanding was that the increase in tire width that my car has should significantly increase grip and braking performance. Could you provide reasoning on why you believe that it should only result in a small increase in grip? For context the car comes with 17x7" wheels with 215 wide tires OEM, while my car has 17x10" wheels with 255 wide tires. That means my wheels are ~43% wider and the tires are ~19% wider. While I have not measured the tire temperatures I know that I am capable of getting them quite warm as I have even gotten them to the point where they felt overheated.

My desire for increasing thermal capacity is a common sentiment in the S2000 community as it is common to crack rotors and burn through pads relatively quickly when using the car at the race track, which I have experienced myself. Personally I have upgraded the pads to a more track capable compound (Endless ME20) which has reduced a lot of the brake fade that I was experiencing. However, I believe my brakes are enduring a lot of heat as the rotors and pads wear quite quickly. From looking at the experience of others, I have noticed that after upgrading to a system with better thermal capacity they are spending less time and money changing rotors and pads. Perhaps installing brake cooling ducts could have a similar effect, but I don't like the idea of having those installed on a street driven car.

Unfortunately Tires are much more complex than increasing the width = increased grip. We do discuss this in the course but to reiterate, if all your doing is increasing the width then for the same tire pressure the contact patch area likely won't change much, but it will change shape and get wider and probably shorter. This could help lateral grip (cornering) but not longitudinal (braking and acceleration).

Also like Gord mentioned temperature comes into play and maybe has the biggest impact of all. With all the different compounds and constructions, sizes, loads and so on it's impossible to give a general rule that increasing the width by X will increase your grip by X.

So this is why the calculator is based on the deceleration G force. which accounts for all of this.

From what you've said, it sounds like you likely have temperature problems with your discs. Is the only issue you're experiencing accelerated wear, or are you also overheating the fluid? I agree it's best to avoid the headache of ducting on a street car - maybe there are some air-guides that could help though?

Otherwise larger discs and possibly a change in calipers sounds like a reasonable next step, with a change of wheels and tires as well.

Since you're keeping the car in relatively stock configuration it's worth looking at some off the shelf kits. See if you can use the calculator to get an idea of the effect they might have on bias - understand that your looking for a slight shift forward. (many Big brake kits have huge rear brakes as well which is often a step in the wrong direction).

Also i'd talk to the s2000 community, people running similar setups who actually use them on track.

Thanks for reiterating the effect of tire width on contact patch. Tires are definitely a subject that I have difficulty reasoning about.

Yes, I am only experiencing accelerated wear and was experiencing fade until I stepped up to a more aggressive brake pad compound. I am not overheating the fluid as I have been careful about using fresh high temp brake fluid.

Your assessment sounds right -- I'll first take a look at some air guides and if those don't do the trick I'll look at off the shelf brake kits that have slight shift forward in brake bias.

Thanks!