Larger Diameter Wheels In Rear
Discussion
The S4s' and V8's have larger diameter wheels in the rear than in the front. The others do not.
Vettes also have this configuration. Ferrari's do not.
Why?
Wider wheels I understand. Larger wheels I don’t.
…unless this allows for a wider yet thinner tire, thus providing additional traction while maintaining stiffness.
That's my theory, what’s the truth?
Luke.
PS, if plus sizing an se/s4 what's the best config:
+0 front +1 rear?
+1 front + 1 rear?
+1 front +2 rear?
Vettes also have this configuration. Ferrari's do not.
Why?
Wider wheels I understand. Larger wheels I don’t.
…unless this allows for a wider yet thinner tire, thus providing additional traction while maintaining stiffness.
That's my theory, what’s the truth?
Luke.
PS, if plus sizing an se/s4 what's the best config:
+0 front +1 rear?
+1 front + 1 rear?
+1 front +2 rear?
question, if the outside diameter of the tire is equal, then how does the diameter of the rim make any difference on contact patch or gear ratio's? The o.d. is the only thing that really makes a difference unless you are referring to sidewall height and stiffness. The comment on the front wheels makes sense though, the less weight the better the unsprung weight which will make the suspension actuate faster and be more responsive.
usa s4s after around no. 3095 i think were changed to the 17 18 combo with the fender flares. the cars before 3095 have 17 and 17 but the same wheel style as the 17 18 combo without the fender flares. you can see the s4s without flares on the home page, you cans see the s4s with flares andrec 1996 s4s on lotusespritworld...
karmavore said: I'm with Chirs, if you want more grip install WIDER tires, not LARGER ones.
Makes no sense to me.
Luke.
You are thinking strictly in terms of enlarging the contact patch width. A larger diameter rim (and therefore tire) also strecthes the contact path front to back slightly.
Mike
you should keep the same rolling circumference ie the large the rim the smaller the tire height, this also means the contact patch should not be any longer or shorter. The contact patch will only alter if you change:-
1) Rim Size and do not decrease the tyre height, therefore change the rolling circumference. (length of contact patch)
2) The width of the tyre. (width of contact patch)
3) Increase or decrease the tyre pressure. (contact patch area)
4) Vehicle weight.
The larger the contact patch, the more force that can be generated for turning, acceleration and braking
>> Edited by dictys on Wednesday 21st May 16:15
1) Rim Size and do not decrease the tyre height, therefore change the rolling circumference. (length of contact patch)
2) The width of the tyre. (width of contact patch)
3) Increase or decrease the tyre pressure. (contact patch area)
4) Vehicle weight.
The larger the contact patch, the more force that can be generated for turning, acceleration and braking
>> Edited by dictys on Wednesday 21st May 16:15
chrislotusatl said: question, if the outside diameter of the tire is equal, then how does the diameter of the rim make any difference on contact patch or gear ratio's? The o.d. is the only thing that really makes a difference unless you are referring to sidewall height and stiffness. The comment on the front wheels makes sense though, the less weight the better the unsprung weight which will make the suspension actuate faster and be more responsive.
Didn't I use the phrase "overall diameter"? Oh, I did.
yeah, but how do you create a "longer" contact patch? If something is rolling the contact "patch" is continuous, no longer or shorter unless under extreme acceleration or decleration which would just increase the total contact patch of the tire. Width yes, length from front to back I do not understand.
Hi,
When you go plus: 1, 2, 3, or 4, you are not increasing the overall tire od. You are simply changing the aspect ratio for the larger rim diameter. What a tuner does is when you increase the the rim diameter, it enables you to actually put a wider tire. And example would be if you had a 275/40-17 on a 17 x 9 rim and you wanted to do a plus 1, then you would get a 285/30-18 on a 18 x 9 rim. The overall od is the same but the contact patch is larger.
I hope I confused you more. For me, I just make sure I get the correct OD, then I get the widest and largest configuration, then I make adjustments to my driving technique and I change the sizes of tires and rims accordingly with respect to applicable rim width.
When you go plus: 1, 2, 3, or 4, you are not increasing the overall tire od. You are simply changing the aspect ratio for the larger rim diameter. What a tuner does is when you increase the the rim diameter, it enables you to actually put a wider tire. And example would be if you had a 275/40-17 on a 17 x 9 rim and you wanted to do a plus 1, then you would get a 285/30-18 on a 18 x 9 rim. The overall od is the same but the contact patch is larger.
I hope I confused you more. For me, I just make sure I get the correct OD, then I get the widest and largest configuration, then I make adjustments to my driving technique and I change the sizes of tires and rims accordingly with respect to applicable rim width.
A few comments:
- The examples you gave (275/40-17 and 285/30-18) do not have the same outer diameter. In fact the 17-in tire's o.d. is almost one inch larger than the 18-in. Perhaps you meat to say 285/35-18 which is only 0.2 inches different.
- There are limits to what tire width you can put on a certain width rim. These vary from one tire manufacturer to another. You should consult the tire manufacturer's web site for fitment information. Most of them include a chart that lists the range of wheels widths that a specific tire can be mounted on. This chart also shows what width wheel was used when the measurement on tire width was determined. Many people do not realize that the same size tire will have a wider contact patch when installed on a wider rim.
- Tire widths are measured from sidewall to sidewall. This means that two different tire manufacturers can have a 275 width tire and yet the contact patch of one can be wider than the other. The same thing happens with o.d.; the diameter of two different brands tires with the same size specification can be quite different. Again the manufacturer's charts will show the real world data for the actual tire you're interested in.
Cheers,
Karl-Franz :-)
www.espritfactfile.com
>> Edited by karlfranz on Friday 23 May 01:01
- The examples you gave (275/40-17 and 285/30-18) do not have the same outer diameter. In fact the 17-in tire's o.d. is almost one inch larger than the 18-in. Perhaps you meat to say 285/35-18 which is only 0.2 inches different.
- There are limits to what tire width you can put on a certain width rim. These vary from one tire manufacturer to another. You should consult the tire manufacturer's web site for fitment information. Most of them include a chart that lists the range of wheels widths that a specific tire can be mounted on. This chart also shows what width wheel was used when the measurement on tire width was determined. Many people do not realize that the same size tire will have a wider contact patch when installed on a wider rim.
- Tire widths are measured from sidewall to sidewall. This means that two different tire manufacturers can have a 275 width tire and yet the contact patch of one can be wider than the other. The same thing happens with o.d.; the diameter of two different brands tires with the same size specification can be quite different. Again the manufacturer's charts will show the real world data for the actual tire you're interested in.
Cheers,
Karl-Franz :-)
www.espritfactfile.com
>> Edited by karlfranz on Friday 23 May 01:01
chrislotusatl said: yeah, but how do you create a "longer" contact patch? If something is rolling the contact "patch" is continuous, no longer or shorter unless under extreme acceleration or decleration which would just increase the total contact patch of the tire. Width yes, length from front to back I do not understand.
OK, imagine you have a wheel and pneumatic tyre in front of you, at the bottom there will be a flat patch where it touches the ground. This is the contact patch. If you scale the wheel and tyre the length of the flat bit changes in proportion. If you double the diameter and you'll double the length of the contact patch. Of course it is more complex than that, but you should get the idea.
karmavore said: I now see how a bigger (larger dia.) tire gives more cp, thanks.
Now back to the original question...
Why do some cars (Vettes, Esprits) ship with larger rear wheels and some not (Ferraris)?
Luke.
The question should be why do they have smaller front wheels and it's because the Ferrari engineers are more concerned with looks than handling and steering feel.
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