38 replies to this topic

[sixspeed]

So... I'm thinking of doing some things to the VX.. and one idea is to go with a 16" wheel. Is there an advantage to going with the 16" front, 17" rear setup? What about 16" all round (would have thought this would be more balanced?) Also, I'm thinking of going for 7/7.5x16 at the front and 8/8.5x16 at the rear.. anyone know what offsets I'll need to maintain the clearance of brake calipers etc and give the best ride/handling? -andy-

[sixspeed]

40 views and no comments? I know there is some information to be found by using the search, but it mainly covers using standard wheels or the OZs etc. As I'm looking at moving away from the "norm", just want to be sure what the correct parameters should be... -andy-

[Ratspants]

40 views and no comments?

(What's wrong with the 16" front/17"rear wheels that every other Elise and derivatives use? Surely this is a proven formula?)

Edited by Ratspants, 29 September 2005 - 11:43 AM.

[sixspeed]

40 views and no comments?

(What's wrong with the 16" front/17"rear wheels that every other Elise and derivatives use? Surely this is a proven formula?)

Well that's my point in asking the question.. If that truely is the best option then I'll go for that setup - but then if it's so good, why do our cars run 17" all round? Perhaps the weight of the VX means that 17s all round are better?

On the other hand, looking at it from a different angle, if I go for 16"s on the front, why do I need 17" on the back? Why not 16" on the back as well?


-andy-

[Smiler]

think that all matt blk euro race car has 16's all round... give Lotus £1m to find out in RnD for you.... or... go with 17 rear 16 front like they seem to put on all elises...

[Ratspants]

What's wrong with the 16" front/17"rear wheels that every other Elise and derivatives use? Surely this is a proven formula?) 

If it's so good, why do our cars run 17" all round? Perhaps the weight of the VX means that 17s all round are better?
...
Why do I need 17" on the back? Why not 16" on the back as well?

I'm certainly no expert but in the absence of anyone else I can try and recall what I've read on here over the years:

The VX has 17" fronts instead of the 16" that the elise and exige come with purely for aesthetic reasons. Some marketing bod really did think they would sell more cars as people liked big numbers and it looked pretty.

The Elise has 16" front and 17" rear as presumably this gives the "best performance" - it seems reasonable to assume that Lotus would put 16" on the rear or indeed 13" all round if they thought it improved the car's performance. I'm guessing that the taller sidewall on the front gives more feedback and better control and the shorter sidewall on the back makes for a more predicatable rear? Need someone with some track setup experience to throw some light on it...

Ben

[garyk220]

Which tyre are you planning on fitting to the rear? You'd need to increase the side wall profile to a 225/50x16 to maintain the rolling diameter within an acceptable tolerance, and therefore keep the speedo/odometer working correctly. Next question is, are there any decent 225 or 235 tyres in this profile. 225/45x17 is widely used on many preformance cars, so there is a good selection of tyres available.

[sixspeed]

I was thinking of something like 195/45-16 on the front, and 215/40-16 on the rear, which I can find Toyo T1-Rs, Goodyear F1s and a few other decent performance tyres in... Can go down to 195/40-16 and 215/35-16 but limits me to Dunlop P9000 or Conti Sport Contact2s..... Is the speedo not connected to the front wheels anyway, so therefore making the 16" change up-front more important than what happens at the rear as far as speedo-accuracy is concerned? -andy-

[garyk220]

Speedo reading is driven by the nearside rear wheel speed sensor. Working from memory here, but the 195/50x16 front tyre is about 3.7% lower rolling radius compared with the standard 17" front wheel. The two options you mentioned 45 and 40 profile tyres are lower again. Probably around 7-10% lower than standard. Fairly sure you'd get problems with the ABS even under normal braking running these, since I recall reading the ABS system is designed to allow up to 7% slip in wheel speeds. With these tyres fitted, I'd imagine the system would think the fronts are locking even under normal braking. Your best bet is to find an on-line tyre size calculator, and muck around with a few tyre and wheel sizes All things being equal, I'd want to maximise the rear traction, so would prefer to fit the widest suitable tyre possible on the rear. PS Not even mentioned tyre load rating, which is another very improtant factor on the VX/Elise. Most of the tyres you've mentioned will probably have a higher load rating, and therefore stiffer side wall, than the Lotus and Vauxhall specific tyres.

Edited by garyk220, 29 September 2005 - 01:05 PM.

[Thorney]

One reason why higher sidewalls are used on light weight cars is to get heat into them by allowing them to flex more. 'Rubber band' tyres on a light car would barely reach decent operating temp as the flex would be minimal, you could compensate this with softer material but that would compromise wear. Look at Caterhams, you run as small a wheel as possible with a higher profile for that reason. Allowing for some sidewall flex also allows for firmer chassis and suspension set ups. The 16"/17" is something that I've simply deferred to Lotus and their vast handling knowledge in that the chassis was designed for the 16"/17" set up and the race cars all seem to like it. If it aint broke then don't fix it I've driven a VX on 18" all round and hated it, it felt heavy, ponderous and slow to turn although at speed this was less noticeable, it certainly felt less agile (IMO anyhoo).

[sixspeed]

Ahh interesting...! Didn't realise about the way the ABS functioned, or the speedo-pickup... Yeah, will take a look at some of the Tyre calculators .. (remember there was a good one linked over from miata.net from my MX-5 days)... Going back a bit, when people have fitted the 16" fronts and 17" rears (OZs?), what size tyres have people been going for, and also what size are the wheels? 7x16 and 7x17? -andy-

[meldert]

I actually use 15" (OZ superturismo) all around for track day use. The reason for this is thats the smallest that actuall fit and it give low weight. Tires are also cheaper, I use Bridgestone RE540s (Yokohama A048 equivalent) 195/55-15 front and 225/50-15 rear this gives a 4.5% (5% difference is the legal limit in Sweden) less radius then the standard setup. The ABS seems to cope fine with this. Edit to add: The aformentioned tyres cost the equivalent of £70-75 per tire in these sizes... Which is al lot less then in sizes 16" and 17".

Edited by meldert, 29 September 2005 - 02:37 PM.

[Arno]

ABS should stay happy as long as you keep the difference between front and rear within limits. As long as it 'sees' all 4 wheels spinning at (about) the same speed it will be fine. It's not the absolute wheel size, but the relative front-rear difference which will trigger ABS problems (on any ABS equipped car, not just the VX) Speedo will be off if you fit really small wheels and tyres, but ABS will work fine as long as the front and rear rolling radius are close or identical. BTW.. Originally the S1 Elise design called for 13 or 14" wheels, but they could not fit the (MMC) brakes they wanted inside the wheels, so they scaled up to 15". Marketing then liked the 'staggered' approach and the S1 ended up with 15/16" For the S2 Elise marketing pushed the 16/17" combo, but this was less of an issue as with the S1, because now they could have suspension and tyres tailor-made for the car. Engineers still wanted to keep it 15/16" though from a handling/suspension viewpoint, but that didn't happen. The S1 tyre choice was always an off-the-shelf compromise (Pzero's were not designed for the S1), which also impacted the suspension design. Speedster/VX got 17" front wheels because a GM designer indeed thought that going to 'bigger wheels' all around would make the car look better. Choice was purely cosmetics in this case. Bye, Arno.

[meldert]

ABS should stay happy as long as you keep the difference between front and rear within limits.

As long as it 'sees' all 4 wheels spinning at (about) the same speed it will be fine. It's not the absolute wheel size, but the relative front-rear difference which will trigger ABS problems (on any ABS equipped car, not just the VX)

Ahh... ofcourse... it's the difference between front and rear that matters. In my case that is no problem at all since both front and rear wheel diametre decreases by 4.5% So the relative front-rear difference will still stay the same...

[juj_singh]

Mate, it seems really stupid to consider fitting 16's all round. Its like saying, "Lotus have spent £££'s finding 16F/ 17R the best combination but I think for reasons unknown that 16's all round is better" This idea's a non-starter.

[ShinyAndy]

That's like saying why remap the engine when Vx/Lotus have spent millions developing the standard map Just because a manufacturer does something it doesn't mean it's for the best for everyone

[Thorney]

when Vx/Lotus have spent millions developing the standard map

/spits coffee over laptop

[ShinyAndy]

[juj_singh]

That's like saying why remap the engine when Vx/Lotus have spent millions developing the standard map

Just because a manufacturer does something it doesn't mean it's for the best for everyone

I assume you'll be putting 16's all round on your car then?

[juj_singh]

You seem to reply without thinking, in this instance are you denying it would be a stupid move to replace the standard wheels with 16's? Your avatar says it all Andy, you are a...........