I'm looking for replacement rubber to go on my GSXR powered Indy. It's currently on ridiculous Yokohama 205/40 R17's all round hat was
on it when I inherited it. I've bought some 15" wheels now and would like to fit some TR1's.
Problem: 195/55 R15's (same rolling dia) seem to be quite scarce and significantly more expensive than 195/50's but these would give a much
smaller dia.
Question: I want improved ride but would the taller side wall of the 195/55's be detrimental to the handling ?
Suggestions welcomed. Thanks.
NB I am pretty sure 205/50/R15's would foul the rear suspension
quote:
Originally posted by Yellow Peril
T1R
R888 medium compound for summer road and track works well, personally recommended. Have 3000 miles and about 7 trackdays in my current set with still a lot of tread left. Otherwise for winter use both on and off track I'd go for normal road tyres or a softer compound track tyre. The thicker sidewall would be okay but would change your gearing/max speed. Personally mine is geared for a top speed of 130 which is about right, worth checking.
Put some Toyo T1R 195 55 R15's on the rear today with 185 55 R15's on the front running at 19psi and 17psi respectively and to say it has transformed the car would be an understatement. Very happy.
What age where the yokos you took off, or do you put the transformation down to the increased profile?
The improvement is definitely down to the smaller wheel down to 15" from 17" and increased side wall height - up from 82mm to 107.3mm on the
rears.
I made changes in stages:
i) reduce pressures in 205 40 r17's all round down to ~20psi from 30 psi
ii) replace front's with 185 55 r15's at ~ 17 psi. Tyres are part worn Kumo's
iii) replace rears with 195 55 r15's at ~ 19 psi Toyo T1R's
I'd say i) made a virtually undiscrenable difference, ii) made a 25% contribution mainly to the steering 'fluidity' whilst iii) had the
biggest overall impact.
My main concerns before making the changes where the very fidgety ride & tramlining and twitchy steering. I just wanted to share the fact that I
have found others comments re tyre-wheel size being critical to be correct in practice.
The front end is still a bit bumpy (3 clicks from softest) so I may try yet lower pressures - How low do people go ???
For what it's worth i'm inclined to say that for sensible road use then it's unlikely you'd notice the difference between a good
and a brilliant tyre on the front.
Rightly or wrongly I run at 18 on the front 16 on the rear, running 185/60R13 all round.
The car is mainly used for autotests, as well as around 3k miles a year on the road. There not a lot of science to the pressures other than it appears
to give fairly even wear and its about half the pressure you would put in a road car of twice the weight, hence should give a simular contact
patch.
Daniel
I run a road going r1 indy on 195/55/15 r888s, was told by the tyre supplier to run 14psi cold as the car doesnt weigh very much which should give you 17-18psi when warm and find handling/grip better than when i got the car (was running 20psi cold) just have a play around with the pressure till you feel happy would be my suggestion.
That's interesting..I suppose pressures will depend somewhat on tyre wall stiffness and how they appear to wear.
I am guessing R888's have a less rigid wall than T1R's which will be less rigid again than std road tyres (I am running Khumo's on the
front)
14psi sounds ultra low..at what point do you run the risk of the tyre of the tyre coming off the rim ? I suppose less likely but potentially more
catestrophic if at the front..
I'm wondering whether I should tinker with my suspension and tighten up by a few clicks now that the tyres are absorbing some of the noise.
I just returned from silverstone where with r888s running at about 60 degrees C, turned a cold pressure of 14 psi into a hot pressure of 17. No problems and tyre wear was constant. I run 17 psi cold for road use though!