18inch wheels up front for trackwork - DC5 specific?

[plAythiNG]

Considering using 18inch wheels up front and 17 inch in the rear for track work in DC5.

Benefits of using a larger rim/tyre combo up front?

[wpg81]

Be aware that this may effect the abs with out changing tyre profile to achieve even circumference front to back.

[mugsee]

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[sleepingperformance]

The main benefit is that you will be able to run bigger brakes ie: 6 pot calipers with a 355mm rotor instead of a 4 pot with 330mm rotor.

The main thing you want to look at is the width of the wheels front to back. Wider at the front and narrower at the rear will reduce rear grip which can reduce understeer in its own right and depending on spring rates & swaybar selection, can increase lift off oversteer.

[benson]

18' will be fine if you have serious HP or traction issues.

Choosing the correct width/offset and tyre size is critical to getting it all work well.

Bigger is not always better.

[mugsee]

Benefits of using a larger rim/tyre combo up front?

I see the true benefits as more tyre choice when compared to 17" tyre sizes. 18" at the front allows you to choose from bigger tyre sizes, which leads to more front end grip and less understeer. Bigger tyres also means that they'll be slightly harder to heat up but also harder to over-heat when pushing.

Something else to consider: what spring rates are you currently using? Would they be stiff enough to control the extra tyre?

[ChargeR]

I'm not going to lie, I'm a big fan of big wheels and have pushed certain other members to go to 18" front wheels. There are many things to be considered though, I look at 18" front wheels as providing three main benefits:

- Wider section width tyres with correspondingly wider wheels. Up to 295mm in DC5 friendly diameters which gives two main benefits: For a given tyre compound there's plenty of evidence that suggests that a wider tyre will be able to develop higher peak lateral grip for the same vertical load. I've never heard of a front wheel drive racer that wouldn't mind a bit more front grip. Secondly the larger and wider front tyre aids tyre temperature management ie. If you're overheating a 225 section width tyre at the front while the rears are still at a comfortable temperature then a wider front tyre will correct this.

- Larger diameter wheel gives smaller sidewall with correspondingly less sidewall compliance, giving a more responsive tyre and the potential for higher lateral grip. This is less important on our relatively lightweight cars though I believe compared to the first two factors.

These positives need to be managed against the negatives though, there's no point going to an 18" 295 tyre and running a hard compound that will never reach optimal temperature on your D series powered CR-X. Likewise if you want to run a 225 tyre there's little reason to go to an 18" wheel.

The main benefit is that you will be able to run bigger brakes ie: 6 pot calipers with a 355mm rotor instead of a 4 pot with 330mm rotor.

The main thing you want to look at is the width of the wheels front to back. Wider at the front and narrower at the rear will reduce rear grip which can reduce understeer in its own right and depending on spring rates & swaybar selection, can increase lift off oversteer.

I'd consider that to be far from the main benefit, just a nice side effect. You can fit plenty of brake under a 17" wheel. You would have to have big power to need more than a 330mm rotor with a 6 piston caliper, which fits under a 17" wheel on a DC5. I'd even go so far as to suggest that it's unlikely an NA 2 litre DC5 will really need a larger rotor than 330mm for heat management reasons, and if heat was a problem I'd be more inclined to look at changes that require less negative tradeoffs such as increasing rotor thickness, pad compound selection and ducting.

Anything that increases front grip has the potential to increase lift off oversteer, but lift off oversteer is more heavily affected by suspension changes that affect the rate of dynamic load transfer such as springs, swaybars, dampers and even roll centre or other geometry changes. A static change like tyre width is more likely to make the car more oversteer biased in all conditions, not just under forward load transfer and pitch.