MK1 with German Autostyle bodykit / GOT PICTURES OF IT NOW

[djdna2000]

I've heard this said about a lot of cars, but never seen any real explanations given as to why, when most racing cars use the absolute biggest wheel they can. Here are my thoughts:

I want as much tyre on the road as possible, to this there is no argument. Given that the stock (185/60/14) rolling radius of 577.6 mm isn't all that different from a 255/40/17 combo on the rear (635.8 mm) and also given that 255/40 tyres have a much stiffer and shorter sidewall, how can it be worse? I suppose the only problem could be the sidewall not offering enough 'give' to keep the whole tyre surface on the road under high-g cornering, though I would have thought this could be sorted with camber adjusting bolts.

whaddya reckon?

[Icsunonove]

....when most racing cars use the absolute biggest wheel they can.

Errrrrm Formula 1?

I want as much tyre on the road as possible, to this there is no argument.

I disagree with that. Depends on contact pressure and coefficient of friction.

I don't have any technical answers. All I do know is the feel and handling of my car is much better with the 14" wheels fitted in my opinion

However I have heard people telling me that their car handles perfectly well on 16" wheels. So maybe it's just personal preference.

Best regards,

Tom

[djdna2000]

Errrrrm Formula 1?

FIA regulations state that Formula 1 cars must have 13" wheels.

[tonigmr2]

I've heard this said about a lot of cars, but never seen any real explanations given as to why, when most racing cars use the absolute biggest wheel they can. Here are my thoughts:

I want as much tyre on the road as possible, to this there is no argument. Given that the stock (185/60/14) rolling radius of 577.6 mm isn't all that different from a 255/40/17 combo on the rear (635.8 mm) and also given that 255/40 tyres have a much stiffer and shorter sidewall, how can it be worse? I suppose the only problem could be the sidewall not offering enough 'give' to keep the whole tyre surface on the road under high-g cornering, though I would have thought this could be sorted with camber adjusting bolts.

whaddya reckon?

OK MK1s I've driven with larger wheels - they tramline horribly, the steering is less direct, the ride is harder and crashes the suspension (standard mind) and generally the car 'feels' less communicative. I guess it's a trade off between more 'contact patch' vs. driver feel.

Also I have to say this - 17s look slightly ridiculous on a MK1 IMHO - like it's on stilts!

T

[djdna2000]

Isn't tramlining down to tyre width though? And tramlining just highlights the fact that you can feel the road more, which can't be a bad thing.

My GT4 was miles better with 225/40/18 than with 215/50/16 (stock). Admittedly the alloys (OZ superleggera) were lightweight, the usual increase in upsprung weight could be an issue.

I can't do anything about the way the car sits of course

[Icsunonove]

OK MK1s I've driven with larger wheels - they tramline horribly, the steering is less direct, the ride is harder and crashes the suspension (standard mind) and generally the car 'feels' less communicative. I guess it's a trade off between more 'contact patch' vs. driver feel.T

That's exactly what I mean, well said T! The steering is heavier, the feedback is dreadful and it understeers horribly

[djdna2000]

I wonder if there is anyone on here that actually knows the answer to this debate? As we are all just guessing.

If it understeers too much then increase the rear ARB thickness, or increase front tyre width, fit a brace on the lower front frame etc.

[tonigmr2]

Oh yeah I forgot about the understeer - present on a MK1 anyway and madly accentuated on vastly bigger wheels. Ask Lauren, she tends to have the technical answers

The best compromise is 15s mate. Now they IMHO do tend to improve the handling over standard.

T

[Icsunonove]

Interesting T.

When I've worn out these 16" tyres, I'm going to sell the wheels. I may buy a set of 15" wheels to replace them then. (And if you're wrong I'll make you pay for them )

[djdna2000]

Are you talking about keeping near-stock widths with varying size diameters though? As I need wider tyres. The damn thing spins the wheels now with the stock red top, what it would do with 300 lbf ft going through it is anyone's guess. I simply need more rubber. So with that as the starting point, I need the best and cheapest way to proceed. If someone can present me with the technical case for keeping smaller then I'll do that, I'm not trying to be argumentative here. But they need to fit some decent brakes under, so at least 16 I would have thought. If I have to fit power steering to the front to move the damn things then so be it

I'm also gonna make/buy some sort of front splitter for extra downforce - Toni was it you who knew someone who had developed one?

[djdna2000]

Interesting T.

When I've worn out these 16" tyres, I'm going to sell the wheels. I may buy a set of 15" wheels to replace them then. (And if you're wrong I'll make you pay for them )

I'm gonna buy some 20" chrome spinners and prove you all wrong

[Icsunonove]

Probably Lauren is your best bet to answer this I'd imagine. I wouldn't go too wide on the front tyres, but that's just my opinion.....

[tonigmr2]

*cough* look at my car in the garage mate.

15" wheels on the twincharger - I got an AP kit designed to go under them if it's brakes you are after!

Also did a bit of cutting for front downforce too - I'm expecting 300lb/ft too

T

[djdna2000]

Yeah, your car looks absolutely amazing. Sadly my budget won't stretch to AP, I'm thinking ST205 or M3 stockers tbh. How wide are you going at the rear? After the grip of the GT4 the thought of more power with less rubber is scary!

[tonigmr2]

Well...195s all round. I used to be a bit wider on the rear (205s) but it didn't make any difference.

*shrug* if it's scarey then I'll have VFM, LOL

Downforce is something you really do need to think about, IMHO the front end is horribly light at speed on the MK1 - hence all the effort I've gone to with cutting and putting a vent in etc.

T

[djdna2000]

I'm deffo gonna do the bonnet/bulkhead mod for flow, and make/buy a LOW front splitter. I had thought about some rudimentary ground effects and an aperture at the bottom of the splitter, but whether I get round to that is another matter. I'm probably buying PW's Ohlins off him which are fairly stiff, this will mean I haven't got to worry about bottoming out the splitter.

I'd recommend some special industrial race pants with all that power through 195s

[tonigmr2]

A few more mm of tyre won't make that much difference, I am adamant I will be sticking to 15s and 205s is the widest I could realistically go - I've also paid a lot of attention to the car's set-up (double adjustable Leda Coilovers) and it will have a Motec which I can use launch control on if I want

Car is lowered as far as is humanely possible without hitting ever speedbump ever made! Have yet to drive it with new front vent set-up, will let you know how it pans out
T
(sorry for the thread hijack!)

[DoM]

....when most racing cars use the absolute biggest wheel they can.

lol, lies!!


Fitting bigger wheels will mean significant changes to sidewall depth/stifness and (possibly) wheel weight, which will affect the handling of the car.

I wouldn't consider them without serious changes to your suspension set up. They may offer you more grip, but destroy the handling of the car.

As everyone has commented, I'm sure Lauren will post the 'techie' reasons.

Besides.. MK1's look like a rollerskate with 17's on!

Dom

[Lauren]

It is, why would you consider that not to be a good idea? (sorry for hijack btw).

Reasons why its not a good idea:

there are some inherent problems with using such sized wheels though and with the necessary low profile tyres they require. You shouldn't mistake roadholding (ie mechanical grip) for handling (what the car does when the tyres are working within their slip angle, ie slightly beyond the limit of grip).

MacPherson strut equipped cars suffer from very poor camber control, with such a low profile tyre as a 17" rim requires, keeping a good contact patch with the road surface is nigh on impossible, so basically you get loads of grip right up until the tyre lets go and then its goodbye and goodnight as you will not have the progressiveness of a higher profile tyre. With a MacPherson strut you really need some movement in the sidewall to allow the tyre to maintain a flat contact patch with the road when the suspension is under compression.

It is for this reason that it is not a good idea to go below a 50 series tyre, such as that which you would put on a 15" rim. Tbh a 14" rim on stock tyres will give the best handling characteristics. You also need to remember that toyota have set the car up to work with the stock rim/tyre setup so it is no surprise that this will work the best in terms of adjustability, stability and predictability and progressiveness.

The other disadvantage of a 17" rim is that of increasing the unsprung weight as more metal means more weight. However, MacPherson struts are very heavy anyway so this might not be as bad as it first sounds, though obviously it does nothing to help.

You will also get far worse tramlining with anything over 195 section in width.

[djdna2000]

Thanks for your input Lauren. Of course I am looking at everything from the twobrutal angle, which is to make everything as big as possible just because, and there can be no better reason than that

I am seriously worried about the lack of traction though, I can't think of any 300 lbf ft cars that run 195s on the driven wheels. I reckon I'd be pretty worried about breaking traction midway through a 3rd gear bend and ending up in the armco

Has to be said though, I found the GT4 on a 40 series tyre to be pretty good on track, and that's a much heavier car with lots of inherent understeer.

Ah well, once I've finished the mk1.5 my next project will be an MR4 I reckon