As above.. i am getting mk indy with a busa engine

iuts coming with some lightweight 13's with 185 front and 205 rear both 60 profile..

I am keeping these and getting some good tyres for when i go sprinting

now all i need is aset of wheels and tyres for hacking around when on the road

found a set of 195/50/15 with nankang ns2-r tyres..

am i going to notice this as a problem running same size all round when on the road??

It seems accepted that light weight 7 type cars are better with smaller (13" wheels with tyres with a larger sidewall profile. That said, many people run 15" and larger wheels and IMHO you would be OK with the suggested tyre size. One other valuable piece of info is tyre pressure, most seem to get better results at lower pressures of 16-18psi per tyre. On my MK Indy I ran 15" wheels and tyres pressures of approx. 17psi. The car was 2.0 Pinto engined and weighed approx. 600 kgs without me, but with a tank of fuel in the MK supplied fuel tank (weighed on a public weigh bridge).

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Originally posted by nick205
It seems accepted that light weight 7 type cars are better with smaller (13" wheels with tyres with a larger sidewall profile. That said, many people run 15" and larger wheels and IMHO you would be OK with the suggested tyre size. One other valuable piece of info is tyre pressure, most seem to get better results at lower pressures of 16-18psi per tyre. On my MK Indy I ran 15" wheels and tyres pressures of approx. 17psi. The car was 2.0 Pinto engined and weighed approx. 600 kgs without me, but with a tank of fuel in the MK supplied fuel tank (weighed on a public weigh bridge).

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That car was always better on 13s. 195s all round will be fine for the road

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Originally posted by Ben_Copeland
That car was always better on 13s. 195s all round will be fine for the road

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I can't remember what offset Olz used to run. You might want to check when car comes before buying any

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Originally posted by Ben_Copeland
I can't remember what offset Olz used to run. You might want to check when car comes before buying any

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The 15s will be about an inch greater on diameter on the front. At the rear they will be near enough the same diameter as your 205s, just slightly narrower. If its for occasional road and they will fit under your front arches ( where they are both wider and taller ) then I wouldn't worry about it.

A friend posted on the Westfield owners club, and i have managed to get a set of 13's same as whats on it with some avon zzr's on perfect..

Excellent, will you be out this weekend then?

All other things being equal, the large rear tyres ought to be giving you a little more grip at the rear, so if the car has been correctly and accurately set up for them then changing to tyres that are the same size all round will result in an increased tendency to oversteer.

If you do find the change in balance is noticeable, then you could look at dialing it out with changes to other settings.

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Originally posted by Ben_Copeland
Excellent, will you be out this weekend then?

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If you fancy a longish drive come down and say hi !

Thanks mate.. Not sure I will Sunday as seeing deadpool with the missus fr valentines love story an all that...
But we will defo have to meet up.. I am doing a Kent coast tmrun starting in Ashford down coast along Dungeness etc in April with the mr2s. ill run in the busa ad ben in his Westfield if ya wanna come along

Yeah, remind me closer the time and as long as its a weekend should be fine

Just bear in mind that if you change the rolling radius of the wheels that you use to measure your speed, your speedo will be out. Larger radius means that your actual speed will be higher than you measure and therefore you will need to be careful around speed cameras.

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Originally posted by SteveWallace
Just bear in mind that if you change the rolling radius of the wheels that you use to measure your speed, your speedo will be out. Larger radius means that your actual speed will be higher than you measure and therefore you will need to be careful around speed cameras.

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Has anyone done any actual back to back real world testing on the effects of tyre size?

Currently my "locost" is running 225/45/16 front and 255/40/17 rear - apart from the actual weight - my rears are pretty heavy (Pro race 1.2's 9" wide), I ignored all the advice on wheel size ages ago as I don't do things by the book. Plus I’m running an engine which will be running over 300bhp, in the donor car the 16" wheels spun up in 1st, 2nd and 3rd in the dry with standard power....

I just wondered if someone had documented the actual differences, say around a track and obtained track times, or is it more a way the car feels and balance?

I always end up referring back to Lotus as they run 16/17 split on the S2 Elise. I suppose my car is more about aesthetics in some aspects than performance.... It doesn’t really bother me as I’d prefer to try something and see what works/doesn’t.

I note a lot of people run the same size front and rear - i suppose it depends on weight, power drive train etc....

Apart from the speedo error, I’d say you won’t notice much difference in grip between a 195 and a 105. The difference in tyre widths on my car is pretty substantial. Plus the tyre wall hardness on decent tyres also comes into play. I had Yokohama S Drives 195/45/16 on the front wheels initially (only as that’s what they had on) I took them off at my mates garage a few weeks ago (Cheers Kirt!) and they popped off, the Yokohama Advan AD08's were a nightmare to get on, so stiff.

I guess I am just saying there are many factors to look at and some real world data (if available) would be useful.

Rob

These are my 1.2's....



Rob