KONVERTER

iTrader: (2)

I know what you are saying Mr. Potato Head, there is less force needed to be put to the wheel to it with the smaller diamater tire.. BUT, the speed difference is not as much because you have to shift quicker when the car gets to the higher rpms' when it isnt covereing as much distance. the car with the smaller diamater tire may reach 6000 RPM's faster BUT at 6000 RPM's the tire will be covering less distance there for will have to shift at hit XXXX RPM to be going XMPH when the other car reaches XMPH at a lower RPM...

bah...

FLY BY Z

I already said that doing this mod by using different diameter tires is not worth is because the negative looks are not worth the marginal performance change.

That is why you use gears and if you think changing gears is "not worth" a difference because of shifting then you have little or no racing/modification experience. Which is cool, man, we all start somewhere.

KONVERTER

iTrader: (2)

oh you must got what im saying all wrong...

i know changing GEARS makes a HUGE difference... but the wheel diamater is a totally different thing... Now if you changed the diamater of the tire to the smaller size and changed the size of the actual final drive gear to compensate for the difference.. the new final drive gear would have to turn the smaller tire 37 more times per mile to acheive the same distance... now since that final gear will need more power behind it to turn the wheel the smaller tire helps it do that....

FLY BY Z

And that is incorrect. Gearing will change tire rotations per mile just like tire diameter. If you change the gearing to compensate you are back to square one. Gearing changes the RELATIONSHIP between how many times the motor turns compared to how many times the wheels turn. So does tire diameter. Think it through or check out www.howstuffworks.com and check out gearing. I am sure it is on that site.

Z Monster

Actually, no. The instruments are oriented as such that the speedo is relative to the front wheel/tire diameter with the tach being relative to the rear wheel/tire diameter. FWIW, you get 4.3 revs per mile more driving a Z with 17"s vs. !8"s from the factory, if you feel like doing more math.

Z Monster

Actually, my center axle in the rear is 4.5 mm closer to the rear fender lip with this wheel/tire set up than stock since I'm running 20mm drop S tunes. The small benefits is that I bring my center of gravity 15mm closer to the ground without having to put on camber adjustable links.

KONVERTER

iTrader: (2)

I understand how that works!

but if you make a smaller final drive gear to spin the wheels more per RPM of the engine then it will need more force behind it to spin the wheel.... but if you make the smaller final drive gear smaller and put smaller tires then it will spin them faster anad need less force behind it to push the wheels the faster...

its like turning a bolt with a socket driver instead of a socket wrench...

KONVERTER

iTrader: (2)

i dunno the speedo goes from the front wheel's.. if it does great...
then why when you peel out the speedo jumps and yer sittin still..

GaryK

Umm, what does slip angle have to do with this? I agree with a possible acceleration advantage, but maybe you could tell me how your setup gives a "slip angle advantage" and why this actually is an advantage....slip angle in a straight line is generally 0 and the term is usually used when referring to tire performance in a turn.

GaryK

oops, double post

FLY BY Z

You are thinking in the wrong direction.

Z Monster

The shorter ground to rim distance with this set up gives a lot less flex r/t the slip angle in quick switchbacks which doesn't have an effect in a straight line as you posted.

Z Monster

I'll dig into the wiring of non-VDC cars and check the service manual.

KONVERTER

iTrader: (2)

when i was driving around tonight i peeled out a few times just to see the speedo jump up to 30MPH while i was going very slow....

and also, vido of cars on dyno shows the speedo accelerating..

Z Monster

As an experiment for your entertainment, I will jack up my car corner by corner and free spin each wheel to see if the ECM picks up speedo data from each wheel speed sensor independently or tandem. That way you will know exactly how off the speedo/odemeter is. However, the benefits of this mod like slip angle advantages and acceleration advantages will still be there. Sorry.

GaryK

Slip angle = the difference between the direction the tire is pointed and the direction the tire (car) is moving. Every tire has an optimum slip angle range at which maximum grip is attained, and for street tires this angle is relatively small. Having a shorter sidewall doesn't necessarily change the optimum slip angles by much, especially when you're talking dot radials.

I think all you're saying is that you believe the feel of the car is improved during transitions since there is less sidewall flex. This is a completely different concept from slip angle. I would agree that it probably is more settled with slightly stiffer sidewalls, but there is not much of a "slip angle advantage". Unless you are using the term slip angle differently from what I've always seen and heard.

On edit: Now that I think about it, I think that the terms slip angle and slide angle have been used to talk about the same thing I'm thinking of, but what you're talking about could be referred to as slip angle. The less deformation due to the construction of the tire, the less "slip angle" you will see...IOW the direction of the tread will be closer to the direction of the wheel. So, shorter sidewalls could mean less tire deformation in turns. I was thinking of slip angle in the context of tread direction in relation to tread direction.

Anyway, the reduced sidewall height can help in steady state turns as well as transitions due to less tire and tread deformation. We're on the same page

Z Monster

I stand corrected (at least on a non-VDC car). The speed sensors on the 350Z that talk to the speedo are on the rear only and operate the speedo independently with TCS on or off. Perhaps the erratic redings on burnout are from the LSD trying to spin both rear wheels at equal speeds. Thanks for the food for thought.