paulf
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| posted on 26/12/07 at 12:36 PM |
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Tyre profile and gearing
I need to fit better tyres to my car for next year as i want to do some track days and the existing ones have little grip and tend to wheel spin in
low gears all the while when abused.Im using 185/70 /13s and have found that most better tyres are in 60 profile so need to go to that.
Im concerned that the overall gearing will end up to low as im using a 3.89 ratio diff and find that 1st gear is only any good for warming the tyres
at present, so with a smaller rolling radius it will be even worse but then the better rubber may compensate. I could fit a 3.54 diff if i can find
one but dont know if it is worth while or maybe I should go up to 15 inch wheels and 195/50 tyres .
My only other option is to use AO21r tyres which may be available in 185/70 /13 but dont know how these will compare to 60 profile? Any thoughts?
Paul.
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worX
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| posted on 26/12/07 at 12:40 PM |
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You could try 205/60's that would not give a great difference in rolling circumference and you would have loads of decent sticky tyres to choose
from in a 13" variety...
Steve
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Aico
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| posted on 26/12/07 at 12:48 PM |
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AO21r is a raintyre. Don't get these for dry trackdays. Do you have an open diff? If so then changing the diff won't cost much.
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paulf
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| posted on 26/12/07 at 12:50 PM |
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Yes have considered that option but may then need to fit new cycle wings, or could go for 185 front 205 rear but worried about ending up with
understeer if i do that.
Paul.
quote:
Originally posted by worX
You could try 205/60's that would not give a great difference in rolling circumference and you would have loads of decent sticky tyres to choose
from in a 13" variety...
Steve
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paulf
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| posted on 26/12/07 at 12:54 PM |
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Im looking for a tyre that is ok for track as well as dry and wet roads, ive heard of caterhams using them successfully. I could change the diff but
need to finfd one first , i have a 4.1 ratio spare but havent managed to get a higher ratio yet.
Paul.
quote:
Originally posted by Aico
AO21r is a raintyre. Don't get these for dry trackdays. Do you have an open diff? If so then changing the diff won't cost much.
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John Bonnett
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| posted on 26/12/07 at 01:48 PM |
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A couple of links that might help
http://www.westfield-world.com/gtc.html
http://www.maserati-rc.org/mrclogin.htm
I notice that you have to register for the maserati site but it is free and the information is all there.
I hope this helps with selecting the correct rolling radius.
John
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worX
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| posted on 26/12/07 at 04:38 PM |
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Westfield use that (sort) of set up:-
185 fronts and 205 rears (or, as above, something similar to that)
quote:
Originally posted by paulf
Yes have considered that option but may then need to fit new cycle wings, or could go for 185 front 205 rear but worried about ending up with
understeer if i do that.
Paul.
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jwallbank
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| posted on 2/1/08 at 09:34 PM |
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Tyre calculator
I've found that this a good site to check wheel and tyre sizes & effects of alternatives:
http://www.tyresite.com/tyrecalc.asp
John W
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procomp
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| posted on 3/1/08 at 09:30 AM |
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Hi using 185 front and 205 rears is perfectly acceptable. If you where using the yoko 048 for instance it effectively gives the same difference as
going from a 185 rear to a 205 rear as changing from a 4.1 to a 3.9 diff if that helps you with any calculations ect.
PS the tyre rolling circumferences listed in DT catalogue are way out by up to 40mm in some cases. I only mention that as that is where many people
get their yoko tyre info from.
What we commonly do is use 185 or 205 for different circuits and if using the 185 also use a set of rear spacers to maintain a setup to give the same
rear grip.
Cheers Matt
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