Open Source Racecar

[Tim.Wright]

did you consider the Kumho Sports tyre range ?
I did use those for my Elise projects -you get a range of compounds the price is low and for trackday and road they are very useful ..

Not directly, though if they make tyres in the size I need I'd consider them. All of the analysis I've done so far (investigating tyre width, rim sizes etc) has been completely independant of the make and model of the tyres.

That said, I have made a list of available tyres from Bridgestone, Michelin, Goodyear and Pielli but this was mainly just to make sure that the sizes I wanted are actually being manufactured.

When it comes to actually purcahsing the tyres (in a couple years I'd imagine), I would not rule out Kuhmo, Continental, Hankook etc...

Tim

[marcush.]

the reason i mentioned this:
The big brands have to allow for the considerable mass of current so called sportscars....I soon realised these tyres did not
work very good with the light Elise.
For some reason Kumhos products offer a very soft construction and this worled very well with Caterhams and Elises.
I have to admit I have not had a hand on this for a few years now -in fact 6years...so I´m not sure if all this is still valid.

[Tim.Wright]

Yea good point, I will keep it in mind.

I've seen Kuhmo's fitted to a KTM X-Bow once at the Nürburgring. There were not many grooves there, looks like quite a focussed track tyre.

If only I had money to get a bunch of tyres tested. Would make the development process a lot more fun.

Tim

[MemroableC]

i would like to through my personal fav tire in to the mix the Toyo Proxes R888's

[Jersey Tom]

Are you concerned about the potential for excessive low-G oversteer with such a rearward weight distribution? What would the contingency be in that case? More tire size split?

Thanks for chiming in Tom, to be honest I am not concerned about low-G understeer because I'm completely ignorant to it. So I understand better, when you say low G are you specifically referring to the linear range of the tyres, or to low steering angles? For example, if the tyres are quite linear to 0.6G, do you speak of the range 0-0.6G, or is there some effect which causes a change in balance at very low levels of lateral acceleration say 0-0.3? Its something I haven't seen before.

Mainly I'm thinking of low G in the sense of when lateral load transfer distribution effects can be neglected, or at the very least where handling is dominated by wheelbase, forward mass distribution, and basic tire properties (effectively these are the assumptions of the stability and control metrics in Race Car Vehicle Dynamics). Generally it will be in the linear range of the tires, sure.

Good bit of research finding the correlation of mass distribution to tire width split though. This may be of interest as well.

As for tires themselves, the possibilities are endless. Suppose it comes down to your balance of requirements, whats available in desired sizes, and cost. I may be somewhat biased but I personally sport Dunlop Z1's on my car as a pretty good max performance summer tire in a wide range of sizes at a fair price. Goodyear's Eagle RS DOT race tires (not to be confused with broad market RS-A's) are pretty sporty as a more race-specific application.

[Tommy Cookers]

isn't the whole point of race cars to operate beyond the linear range of tyres ?

handling is that beyond the linear range, within the linear range it's just steering (and should not be allowed to affect design) ??

[Tim.Wright]

isn't the whole point of race cars to operate beyond the linear range of tyres ?

handling is that beyond the linear range, within the linear range it's just steering (and should not be allowed to affect design) ??

Handling is the whole lot (linear and limit) but you typically split it into the linear and limit regions because they are two completely different animals to analyse.

We are not saying limit balance is not important, its just that the discussion happens to be about linear handling at the moment.

Low speed handling depends on mainly the tyre cornering stiffness, limit handling is more related to the overall coefficient of friction. You can have a car which is US in the linear range and OS at the limit. Its not desirable from a drivability point of view.

Tim

[Jersey Tom]

isn't the whole point of race cars to operate beyond the linear range of tyres ?

Absolutely not. Not by necessity. The point of race cars to go around a track as quickly as possible. That may (and often does) involve running tires at or near the limit of adhesion for some portion of the lap. You're guaranteed however to spend at least some, and generally the majority of a lap within the linear range however.

handling is that beyond the linear range, within the linear range it's just steering (and should not be allowed to affect design) ??

Nope. Don't agree with that at all. Handling is car behavior through the entire span of its operating envelope. Makes no difference to me if it's 0.3G, 1.2G, 4.8G, or whatever.

[marcush.]

kumho ECSTA V700/V70A was the choice :

http://www.kumhotire.de/fileadmin/KUMHO ... sliste.pdf

the pricing is quite favourable as well.. I have to admit in Ferrari Challenge -having direct comparison to Pirelli (both as slicks) it was obviously the more delicate choice and you needed to really be a lot more gentle with the car .....but ultimately the lap times were very close albeit the Pirellis survived a tad longer when punished..

[Tim.Wright]

Thanks for the tyre suggestions.

I think I will do the initial development with normal (but performance) road tyres because there I at least have a bit of a database of manufacturer tyre choices to go with.

Tyres such as Kuhmo, Toyo etc are better tested once I have a running car which is a bit off.

Regardless, all these suggestions are going into my design sheet.

Tim

[Caito]

This is a troll like question, but trust me I'm no troll.

How you came to the suspension pickup points? I'm guessing you have no tire data.
If you don't know push/pullrod or direct connection, how can you design the chassis if you don't know where is that force going?

[marcush.]

This is a troll like question, but trust me I'm no troll.

How you came to the suspension pickup points? I'm guessing you have no tire data.
If you don't know push/pullrod or direct connection, how can you design the chassis if you don't know where is that force going?

I´d guess tim uses the parametric cpabilies of CAD to keep all this adaptable as long as possible? In the old days you would mock up all this in your brains or sketch up (!) some general layouts on a piece of paper till everythimng fits ,but final positioning will be dictated by the real hard points be it regs ,legal requirements or cornerstones you define for yourself (minum rideheights ,ramp angles etc..)

[Greg Locock]

This is a troll like question, but trust me I'm no troll.

How you came to the suspension pickup points? I'm guessing you have no tire data.
If you don't know push/pullrod or direct connection, how can you design the chassis if you don't know where is that force going?

My answer would be that the particular tire selected will have roughly the same maximum force capabilities as any other tire of similar size that is competitive, so precise knowledge of tire characteristics is not required for hardpoint design.

[marcush.]

wasn´t your point the other day that any bolt or adjustability is a weakness of the whole design ?
It´s not very clear to me that all tyres of the same dimension actually want the same geometry layout . Adding to this is the sometimes huge differnce in physical size from tyre to tyre with differing suppliers and models that could or could not play into your plans.

(that´s for example one reason for avoiding pro ackerman -the inside wheel may scrub on the tub too early with steering lock avoiding the use of the wider front tyre or track width)

[Jersey Tom]

wasn´t your point the other day that any bolt or adjustability is a weakness of the whole design ?
It´s not very clear to me that all tyres of the same dimension actually want the same geometry layout .

In my mind it's not the tires that want anything, it's what the designer wants to achieve conceptually. Semantics maybe, but still a distinction.

Depending on what you're trying to achieve I think you could make the argument that some design concepts will have the same effect regardless of what tires you go with (within reason). For example, FLLTD and forward weight distribution.. you have a pretty well known effect that's going to have pretty similar effects regardless of tire selection.

So sure, the absolute target of where you want to be with any of these things is a function of both what the designer wants to achieve and the specifics of your tire choice... but getting in the ballpark and knowing what adjustment range you need shouldn't be a huge mystery.