Wheel sizes for performance?

[grepin]

Does anyone have any theories on the best size wheel suited for performance on a R33 Gtst. Either 17 inch or 18 inch. Believe that 17 inch is actually better due to providing a larger footpat + lighter.

[Abo Bob]

I'd say 18 inch because less side wall flex. You can get lightweight rims of either size but I suppose the 17's would be lighter. That would probably be made up for by better handling from the 18's.

17's use cheaper tyres though...

[Duncan]

I don't think rim diameter makes any difference in practice....

Things to consider are the wieght of the wheel, since a wheel contacts the road thru only the tyre, not via suspension, the weight can make a difference

Sidewall height of the tyre you put on it, like Adam said can make a difference, in theory lower sidewall = less flex. This doesn't really apply for r typre tyres as much since they have super stiff sidewalls anyway.

Width of the rim...you can run wider tyres with wider rims

Strength of the rim...some of the cheaper lightweight rims are not strong enough and can buckle easily.

I think you will find that the quality of the tyres makes a million times more difference than the wheels they are on. Most people buy bigger rims because they look good, not because they make a significant difference to performance, just like a BOV or FMIC

[Sydneykid]

What Duncan said, but some rims are very heavy, like having 4 flywheels.

[dangerous_daveo]

Few strange questions then, why do a number of race cars, ie F1, champ cars, V8 supercars, etc have a fair bit of sidewall to them?

It was explained to me a while ago why tyre is better for a street car. But I cant remember now for the life of me.

[Duncan]

damn good question...dunno!

maybe they take into account the "springing" that the tyre gives as part of the overall suspension....maybe the wheels are lighter by being smaller...but I'm willing to bet those sidewalls are super stiff on those tyres.

Watching a person trying to fit a r tyre to a rim is painful...having to jump up and down on a tyre lever to get the damn thing onto the rim.

[dangerous_daveo]

Im sure it was something to do with suspension and tyre walls. Its annoying me now, but it made a lot of sence at the time, basically anything over 17s was daft for the street.

[SLY33]

id go and say that 17s are the best for performance on a 33. firstly because the weight will be more with larger diameter and also the rolling diameter is usually increased a little bit, even tho its supposed to be accomodated for by running lower profile. The geometry of the suspension was designed to run 16's, and since going from 17's to 19's you realise the car becomes less chuckable and takes on a very different feel, i think mostly coz of the rubber band profile. You have less warning of when its gonna let go.

Thats from my experience, running similar spec street tyres on both the 17 and 19's. Any increase in rolling diameter will also affect braking, probably not by much, but the effect is there. But then from an aesthetic point of view, the 18's might be the best in terms of looks and performance, as 17's look small with a big kit, especially if the cars not dumped!

[geno8r]

17"s

[krzysiu]

18 would be ok as long as the tyres and the wheels diameter is the same as the 17inches, which mean the 18inches would need thinner tyres. If you put it in simpler terms, the smaller the wheels the quicker acceleration although lesser top speed, and too big will give you slow acceleration and a higher top speed. You just have to see for what situation your car will be in. I heard 17 inches are the best, but dont know for sure...

[Bl4cK32]

If any have seen HPI dvd's...there's a drag skyline with 15" rims on it! they had to do something with the brakes if i remember....more sideall flex, just like the funny cars, means traction....

Good topic, because i a looking at getting some RE55s for the 16" Advan rims that came with my R32. I need some serious traction for my rb31

Ho good would some RE55 be on 16*7 rims on the front, and 16*8 rims on the rear, also what would be the best tyre sizes for these rims?

(sorry to hijack a little )

[mokompri]

the smaller the wheels the quicker acceleration although lesser top speed, and too big will give you slow acceleration and a higher top speed...

not completely correct... the lighter the wheel the better the acceleration, top speed is determined by rpm and all the gearing that occurs ie gearbox, diff and the rolling diameter of the wheels

and so in this case, if you get 17" with higher profile, and 18" lower profile, you can achieve same rolling diameter and therefore same top speed, and if they are identical wheels then obviously the 17" will be lighter, less rotating mass = better acceleration

[Laurence]

I think he meant by having smaller rolling diameter of the tyres (not the wheels) effectively changing the final drive ratio.

17" wheels may be lighter, but the tyres will be taller to give you the same diameter so I don't know if the total package would be lighter or heavier (I suspect lighter).

[dangerous_daveo]

not completely correct... the lighter the wheel the better the acceleration, top speed is determined by rpm and all the gearing that occurs ie gearbox, diff and the rolling diameter of the wheels

and so in this case, if you get 17" with higher profile, and 18" lower profile, you can achieve same rolling diameter and therefore same top speed, and if they are identical wheels then obviously the 17" will be lighter, less rotating mass = better acceleration

Yes and no... As far as I can remember there are other things playing in that equation. Such as I seem to remember more air in the tyres make you faster, less air is more grip off the line. Such as at speed the tyre isnt going to have the same characteristics as it would when the car isnt moving, and this I would think would be effected also by tyre size, (ie wheel size).

[Roy]

Id say go for 17" and get as wide as you can fit:)

My thinking is you want to get as light a rim as possible. So going for the smaller diameter wheels helps weight. But with 16" you cant fit much in the way of larger rotors. So i say stick with 17" rims, you can fit up to 330mm rotors rather easily, good compromise of price for rims and rubber, weight and stength.

One thing which im curious about, is there any real difference between the syle of rim and brake cooling. I knwo the basic criteria for race wheels are weight, stregth and cooling

[dangerous_daveo]

From Autospeed I think...

Turns out I was wrong, I was thinking suspension, go softer suspension so the tyre doesnt have to work so hard, mostly the tyre walls. Personally Id still stick to 17s at the max, I feel the sidewall movement, and the added air helps handeling on the street on rougher roads.

"

So, what about tyre pressure? Obviously, tyre pressure plays a very important part, but there are clearly limits on both sides of the tyre pressure equation. At the higher end, there is the maximum tyre pressure that can be sustained before there is damage to the carcass. At the low end, you don't want the sidewall almost collapsing, generating massive heat, and have the tyre slipping on the rim. So, you can play around with tyre pressures to optimise your set-up, but there are limitations.

A simple way to find out approximately what pressure is optimal for your combination is to draw a chalkline across the width of the tyre, drive for a bit, and look at the wear pattern of the chalkmark. Wearing more quickly in the centre indicates pressure that is too high, and wear on the edges indicates too low a pressure.

One issue to consider is that, for wet weather driving, despite what you may have heard, it is better to increase your tyre pressure, not reduce it. The reason is that there is a relationship between tyre pressure and the speed at which there is the onset of aquaplaning. In the Imperial system, the equation is 9 times the square root of the tyre pressure. So, if your tyres are at 25 psi, if you drive into a puddle that is deeper than your tread depth, you will aquaplane at 45 mph (72 km/h), whereas if your tyre pressure was 36psi, you would aquaplane at 54 mph (87 km/h). The advantages are obvious.

As far as tyre profile is concerned, the main benefit is one of handling - the lower sidewalls give reduced sidewall deformation under lateral loading, which results in improved steering response and a more stable contact patch.

Conclusion

Summarizing, what factors are important in terms of tyre grip? Tyre width has no direct relation to the amount of grip generated; it is a secondary factor, and the width basically relates to cooling potential and so the tyre compound that can be used. The size of the contact patch has no bearing on the amount of grip generated at all, apart from the extreme of where the compound is getting so hot that it no longer acts as a solid (and therefore doesn't follow Amonton's Law). The tyre pressure has no direct bearing on the level of grip (apart from aquaplaning), but it does have a bearing on the heating and cooling characteristics of the tyre. Having a lower tyre profile gives improved handling through reduced sidewall stress and improved contact patch shape stability."

Hope that helps.

[mokompri]

i cant see how tyre pressure would not affect grip, as it affects the contact patch greatly, where is that text quoted from ?

if your worried about the increase in weight of wheels, then you can lighten your flywheel, therefore decreasing the overall rotating mass the engine is spinning, although theres quite a bit of maths to find exactly how much to take off to offset the effect of the extra weight from the wheels

although another problem with heavier wheels is the increase in unsprung mass, which theres not much you can do about really

[dangerous_daveo]

i cant see how tyre pressure would not affect grip, as it affects the contact patch greatly, where is that text quoted from ?

....

AFAIK its from Autospeed.

I would read it again, it says tyre pressure effects grip greatly

[FurryBarry]

why do a number of race cars, ie F1, champ cars, V8 supercars, etc have a fair bit of sidewall to them?

As far as I know, the open wheelers use the sidewalls as the major moving suspension component. Ultra tricky sidewall design means it is spring and damper in one. Unsprung weight becomes only the outer part of the tyre.

The aim of suspension (on a racer anyway) is tyre control. This way the tyres control themselves.

Downforce also contributes. More sidewall trickery allows the 100's of kg downforce to squash the tyre and give a larger contact patch than with low stiff sidewalls.

V8 Supertaxis have a 68 profile bag which they need because they run a crap Watt's linkaged live axle rear end. Front end went to double wishbone in 2002(?)but they have to run the same tyre all round.

Off a racetrack, in a road car on 18inch 35 series you get good at dodging potholes.

[Laurence]

V8 Supercar's run 40 series tyres... They are that size for historical/cost reasons only.

You may have read the sidewall of a racing tyre and seen 680... that is the total diameter in mm. Not 68%