The 24 Hours of Lemons Forums → Lemons Tech → wheel size
I was wondering something for a road race course. Our Lemons car came with 17" (Nissan Maxima) wheels and a team mate suggested we consider going to a 15" or 16" to not only lower the car but it effectively lowers the gear ratios to get "better grunt out of the corners".
So presupposing we use the same width tire (I know the tire patch will still be smaller with a 15" vs. a 17" 245/45) but would a smaller diameter tire make the car handle better??
uh... noo? the point of larger wheels is to give it shorter sidewalls without significantly changing the dynamics of the car. this will stiffen the ride up and usually increases handling. another benefit is the area surrounding the brakes get more air space which makes them easier to cool.
15" tires are cheaper.
16s are the best compromise between sidewall flex and handling and availability/cost... decent 225/60R16s aren't that expensive in teh grand scheme of things.
We run 205/50/15's and they are about the cheapest tire you can buy!
235/75R15 
225/50-16 on 7.5" rims here vs the stock 215/60-16 on 6" rims.
I was wondering something for a road race course. Our Lemons car came with 17" (Nissan Maxima) wheels and a team mate suggested we consider going to a 15" or 16" to not only lower the car but it effectively lowers the gear ratios to get "better grunt out of the corners".
So presupposing we use the same width tire (I know the tire patch will still be smaller with a 15" vs. a 17" 245/45) but would a smaller diameter tire make the car handle better??
Yes, decreasing the rolling radius of the wheel/tire assembly will improve accleration and braking response. As you note, the contact patch will get smaller in the longitudinal axis, but that can be made up in width somewhat. This is a free "cheat", since rules allow unlimited tire size/budget, but it's gonna be tough to change diff ratios within a 500 budget.
Going to 15s or 16s with a little more sidewall (relative to the 17s) will also reduce your chances of bending a wheel
ifb_mole,
Changing the rim size of your wheel/tires does not have to affect tire contact patch size or shape. What you need to look at is the mounted tire diameter or revolutions per mile. In our case we started with small 14" wheels and wanted to bump up to 15". Our original tire was a 185/65R14 with an OD of 596mm. We wanted the larger rim so that we would have more tire options and a shorter sidewall to increase stiffness and improve cornering. We chose a 205/50R15 tire that has an OD of 587mm. The smaller tire gave us about 1.5% lower gearing. The wider 205 put more rubber on the road and the shorter sidewall stiffened up the tire.
That said, we also got a deal on some 205/55R15 tires. These tires are slightly bigger OD than our original tire. We were a little worried about the larger tires scrubbing in our wheel wells, but it was not a problem and the cheaper tires worked fine. We did not notice the small difference in gearing. Heck, the car is so underpowered it is hard to notice the engine at all.
Trust me on the tire stuff. I design ‘em for a living.
Whether the wheels are big or small, most wheels aren't allowing much air at all to the brakes anyway. So I wouldn't put a whole lot of emphasis on that.
However the gearing of smaller wheels + tires with a smaller overall diameter is definitely effective and worthwhile for an underpowered car if you drastically reduce the overall diameter. And the taller sidewall of a smaller diameter wheel (if you're trying to keep the same rolling diameter) is not a huge concern with these pieces of crap. Alot of the BMW's, hondas, toyotas, et al. are running 14 or 15 inch wheels and do very well out there. And like Loren mentioned, the tires are much cheaper.
Another thing to consider is smaller wheels and tires provide substantially less unsprung weight. I have very light 225/60-16 BBS wheels and R comp track tires on one of my "real" cars and they are easily twice as heavy as the 195/60-14 setup we have on our 325 Lemons car. The car's suspension and brakes benefit from this by having to react to and slow down less weight (rotational mass & torque moment). Bigger isn't always better when it comes to wheels and tires!
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