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Old April 22nd 2009, 12:53
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what size for ultimate handerling?

few changes happerning with my race car.
going from the 8x15 and 9x15 split rims with full slicks to some road legal rubber.
got a few options but am having a hard time working out what is going to be best.
this is a pure race car but i want it road legal so i cna do testing and shake downs esayer.
the modern trend is to go for the biggest rim you can fit with low profile rubber as aposed to the old school way of a smaller wheel with a higher sidewall.
i need to keep the rolling radius up so it wont mess with the gearing to much so a tyre between 600mm and 640mm is needed
that means 205 60 15/225 45 17

looking at the smaller super rally cars there all running 17/18 rims and super stiff suspension. have aroud the same wieght 750kg but not as much power. i have 150bhp@ wheels.

but looking at the classic porsche rally cars there all on 15" rims with a higher sidewall, i know that the regs mean you cant have low profile tyre.

what i need to work out is in a pure performance term will a 17" tyre and wheel be quicker than 15" one?
car is used for hill climbs and sprints so i need a super sticky tyre and very fast direction changes which lead me to the 17" set up. but talking to a few folk who say that i need some sidewall to allow me to gain some mechanical grip, which means the 15" route.

16" is not a option as the tyres i want to run are ether 15 or 17.

very confusing subject but any ideas?

cheers rob
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Old April 22nd 2009, 13:33
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Hey Rob, long time...

I would say go for the 17". IMO the "mechanical grip" that u were told about results in much more deflection on the tyre it self allowing more suspension movement that in turn results in incorrect angles (at the extremes).
personally i really like the advan a048 very much that also comes in the 225 45 17 dimension u specified.

if u look carefully for tyres u should find a rolling radius and section width dimensions which are useful to calculate final drive ratio changes and clearance in fender/ suspension

Chris
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Old April 22nd 2009, 13:57
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I say go for the smallest diameter rim that will fit over your brakes. The biggest reason to do this is the cost of rubber. If you're looking at street testing that means a semi-slick at best and the smaller the rim the cheaper the tire. I went with a set of 18's to get maximum tire diameter and width (I couldn't find a 285/295 16") but my semi-slicks also cost me over $1600 after mounting and balancing (including a discount). A set of 205 or 225 15" semi-slicks would be half as much at most. There's also rotating mass and unsprung weight to consider, smaller rims are are much lighter and better at almost everything except top end speed where the smaller wheel diameter bites you in the ass.

In all honesty I would rather have a smaller diameter wheel with cheaper tires and better price/performance than larger more expensive wheels. If I could have used 15" rims I would have in a heart beat.
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Old April 22nd 2009, 16:14
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I say go for the smallest diameter rim that will fit over your brakes. The biggest reason to do this is the cost of rubber. If you're looking at street testing that means a semi-slick at best and the smaller the rim the cheaper the tire. I went with a set of 18's to get maximum tire diameter and width (I couldn't find a 285/295 16") but my semi-slicks also cost me over $1600 after mounting and balancing (including a discount). A set of 205 or 225 15" semi-slicks would be half as much at most. There's also rotating mass and unsprung weight to consider, smaller rims are are much lighter and better at almost everything except top end speed where the smaller wheel diameter bites you in the ass.

In all honesty I would rather have a smaller diameter wheel with cheaper tires and better price/performance than larger more expensive wheels. If I could have used 15" rims I would have in a heart beat.
couldn't agree more!

Look around if you can get used slicks for cheap and see if the rims needed for them will fit over your brakes.

Smaller wheels are lighter, but smaller tires are a lot lighter as well!
+The added benefit of the smaller tires being a lot cheaper if you want to buy new ones.

In general: 13-15inch should be fine, depending on what you can get (for cheap), your needs and budget.
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Old April 22nd 2009, 16:27
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this is not about useing what i can get cheap of e-bay a s i know a few rally teams that i can get tyres from.
want i want to find out is the reason ALL modern race /rally teams use the biggest diameter rim,tyre combo that the regs allow?
biggest prob with useing the 13/15 rubber is the overall gearing effect it will have on my car. with the currant 24/58/15 its topping out at 110mph@7000rpm which is not enough.
dont want to change the box as it has only done around 1500mile since being built and is just being fitted with a lsd.
imho the 9x15 rims i have at the moment are too wide for a bug, i dont have the power or wieght to make the tyre work enough to get up to temp so never get the best from the tyres.
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Old April 22nd 2009, 17:35
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Sounds like it'll come down to cost and you should probably do a little more research before deciding. Lightweight large diameter wheels and sticky tires will probably cost as much or more than regearing your tranny. I speak from experience on this.

The reason other guys are running big wheels is because they need big brakes to stop heavy cars without fading. Not the case with beetles where you can get away with small disks. Most of the rally teams I know of (on this side of the pond anyway) are running 15" and 16" even on tarmac unless you're talking wrc but even then I think they top out at 17".
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Old April 22nd 2009, 18:26
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jsut about all group N,A wrc and the super 1600, s200 run 17 or 18 on tarmac
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Old April 23rd 2009, 04:52
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jsut about all group N,A wrc and the super 1600, s200 run 17 or 18 on tarmac
Thats all because of the braking/brakes. Their cars are heavier than ours so they need bigger/more powerful brakes.

On tarmac they have a lot more grip than on gravel (offcourse).
So on tarmac they basically use the biggest brakes possible (AFAIK up to 380mm diameter!), which needs at least 18" (or 17" for somewhat smaller discs), whilst on gravel they use smaller discs (300-320mm) and matching 15" wheels.

Since (as Humble said) 18" slicks are quiet expensive (especially compared to 15" or 13") for someone like us running lightweight cars on a tight(er) budget it is probably smartest to use wheels and tires up to 15".
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Old April 23rd 2009, 05:14
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i agree with $aint on this one. The larger wheels are to allow the potential for super sized discs since they can't run carbon rotors and in general their weight restrictions optimise around the larger discs. With the lower classes there is a bit of blind following but don't forget that modern wheel sizes are tending towards the 17"+ diameters. I think that you shouldn't buck the trend as it will eventually restrict your options. I would go for 17" wheels if you are committed to the 650(ish) rolling diameter. You then have another option at a later date should you need to lower the gearing - fit 15" wheels with low profile tyres @ say 580 rolling radius.

BTW low profile tyres/large dia wheels are heavier than high profile tyres/smaller dia wheels for the same rolling radius so the low profile route will increase unsprung weight that on the front of a bug will have a significant effect. Mind you unsprung weight never slowed the Mk1 and Mk2 Escorts that 30 years on are still winning!
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Old April 23rd 2009, 06:49
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looking at the super 1600 class which is very close on wieght, around 800kg but they have a about 250bhp so a bit more than me.
trying to find decent sticky rubber in 15" in the size i need is proving very hard, unless i want to spend £300 a corner for tyres that i have been told will last around 500 miles if im lucky.
finding sticky rubber for 17" in the size i want is proving much esayer which might be all i need to convince me to go that route.
going the 17" route also means i have the option of going up on brakes should i ever get round to going rallying with it as i dont think the stock braking system i have at the moment will cope with more than a few miles at racing speeds.

cheers for all the ideas and help.
rob
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Old October 2nd 2011, 12:59
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got no race experiance with bugs but had an interesting experiance last 2 rallys i did.

i was running 13" wheels and moulded slicks and was constantly taking time out of an apponant untill the end of the day and we did 2 very long stages and he wipped my but. after discussing it we could only reason that my tyres were going off. i didn`t feel it at the time but we couldn`t reason it to be anything else.

larger tyres will run a more constant temp compared to a smaller tyre which will overheat on long tests.

i also feel too low a profile limits the predictability in the handling and thus limits confidence.

lee.
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Old October 4th 2011, 03:44
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i have now done a practice hill climb with the 17 inch wheels and running track wets. thinking behind the track wets on dry tamac is, the wets are the same compound as the hill climb slicks slicks but i get the wets very cheap.
turn in is very good and stable, braking feels a lor better and the mid corner grip is very high. none of the rolling i used to get on the 15inch rims with the higher profile. corner exit grip is also up but i think thats down to having the lsd fitted now.
the tyres had pretty temps across them[39c to 40c] but still way below what they would run on a track as there only being used for about a minute so never getting really hot, so i'm pretty happy with the them. just have to learn to trust the grip as theres so much more than before.
also the bigger rolling radius has given the engine somthing to pull against which has made it d=feel quicker than it buzzing through the gears like before, wont know till we get the stop watch out and time it.
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