Wheel size V performance

[Graham_Amika]

Does anyone have any information on the effect that wheel size has on performance. Mine is SP6 with 19" wheels so I guess this could mean any of the following (based on simplistic opinion).

1. Marginally slower accelaration at lower speeds but slightly higher top end speed?
2. Improved traction due to more contact surface with road (backs are 9.5" wide I think, which results in no real difference versus smaller wheels when considering larger wheels are maybe a bit heavier?
3. Engine has to work a little harder to turn larger wheels and hence slower?
4. If larger wheels are lighter than smaller wheels (previous owner spent a lot of money on them), maybe faster as car is lighter overall?
4. No difference?
5. Can only tell by carrying out some measured testing,,, but this would be a pain as car is now very much setup for 19" wheels with all suspension geometry all set up.

I would appreciate some advice...

Many thanks
Graham

[carl_w]

Usually as you go up in wheel size you go down in tyre cross-section so the rolling radius remains the same. So, no difference.

Interestingly you won't get better traction either. The contact patch only depends on the tyre pressure and the weight of the car, so with fat tyres you'll just get a fatter, shorter contact patch.

Edited by carl_w on Monday 30th April 20:04

[jensena]

The main - probably the only - reason for fitting 19" wheels is cosmetic, they wont make your car perform better.

[UK_WS6]

Also, wheels with low sidewalls, will have more of a job in the accelaration (sp) dept.
Wheels with taller sidewalls will out perform wheels with say, 35 series cross section, to a wheel with a 60 series cross section, bearing in mind, that there will be a decrease in rim size to maintain the ideal rolling circumference.
Some thing to do with the stretch and the "give" in a taller side wall, thus enabeling an increased contact patch area.

[Graham_Amika]

Thank you for both of your comments, the previous owner certainly liked them, but I'm pleased that they don't make any real difference to performance as I'd be wondering how the car drives with standard ones. Personally I think they look great. With the only draw back that they take too much polishing.

Actually a couple of people have pointed out to me that they are not standard and as such they wouldn't have them...

Is there a purist bias amongst some TVR owners?

[jensena]

Graham_Amika said:

Thank you for both of your comments, the previous owner certainly liked them, but I'm pleased that they don't make any real difference to performance as I'd be wondering how the car drives with standard ones. Personally I think they look great. With the only draw back that they take too much polishing.

Actually a couple of people have pointed out to me that they are not standard and as such they wouldn't have them...

Is there a purist bias amongst some TVR owners?

There is a purist bias sure, but it has a lot more to do with the function of the Cerbera as a car. It's a bisterngly fast supercar, so why fit something that is detrimental to the cars function, just because it looks pretty?

[davidn]

jensena said:

Graham_Amika said:

Thank you for both of your comments, the previous owner certainly liked them, but I'm pleased that they don't make any real difference to performance as I'd be wondering how the car drives with standard ones. Personally I think they look great. With the only draw back that they take too much polishing.

Actually a couple of people have pointed out to me that they are not standard and as such they wouldn't have them...

Is there a purist bias amongst some TVR owners?

There is a purist bias sure, but it has a lot more to do with the function of the Cerbera as a car. It's a bisterngly fast supercar, so why fit something that is detrimental to the cars function, just because it looks pretty?

Do look good though.

[jensena]

davidn said:

jensena said:

Graham_Amika said:

Thank you for both of your comments, the previous owner certainly liked them, but I'm pleased that they don't make any real difference to performance as I'd be wondering how the car drives with standard ones. Personally I think they look great. With the only draw back that they take too much polishing.

Actually a couple of people have pointed out to me that they are not standard and as such they wouldn't have them...

Is there a purist bias amongst some TVR owners?

There is a purist bias sure, but it has a lot more to do with the function of the Cerbera as a car. It's a bisterngly fast supercar, so why fit something that is detrimental to the cars function, just because it looks pretty?

Do look good though.

They do don't they

[Ireland]

jensena said:

davidn said:

jensena said:

Graham_Amika said:

Thank you for both of your comments, the previous owner certainly liked them, but I'm pleased that they don't make any real difference to performance as I'd be wondering how the car drives with standard ones. Personally I think they look great. With the only draw back that they take too much polishing.

Actually a couple of people have pointed out to me that they are not standard and as such they wouldn't have them...

Is there a purist bias amongst some TVR owners?

There is a purist bias sure, but it has a lot more to do with the function of the Cerbera as a car. It's a bisterngly fast supercar, so why fit something that is detrimental to the cars function, just because it looks pretty?

Do look good though.

They do don't they

The 19"'s look good but that style would drive me mad trying to clean them.

I'm lazy when it comes to washing cars so if I could get away with three-spoke wheels I'd be happy.

19" 3-spoke

[Jonnie B]

[quote=Graham_Amika]Thank you for both of your comments, the previous owner certainly liked them, but I'm pleased that they don't make any real difference to performance as I'd be wondering how the car drives with standard ones. Personally I think they look great. With the only draw back that they take too much polishing.

Actually a couple of people have pointed out to me that they are not standard and as such they wouldn't have them...

Is there a purist bias amongst some TVR owners?

Hi there so your car at the PH meet near Leeds a few weeks back, weels look very good. Have you been able to fix the panel in front of the windscreen yet?

John B

[Graham_Amika]

Car is in with SSCC now, for a number of niggles, but funnily enough that panel looks OK and appears to be fixed down correctly. It seems the panel might just be a little bit warped but it isn't a problem.

cheers
Graham

[mackempete]

Hi Graham, you didnt buy that car from a guy called Stephen did you? Had his own timber business?

[Steve_T]

Graham_Amika said:

Does anyone have any information on the effect that wheel size has on performance. Mine is SP6 with 19" wheels so I guess this could mean any of the following (based on simplistic opinion).

1. Marginally slower accelaration at lower speeds but slightly higher top end speed?
2. Improved traction due to more contact surface with road (backs are 9.5" wide I think, which results in no real difference versus smaller wheels when considering larger wheels are maybe a bit heavier?
3. Engine has to work a little harder to turn larger wheels and hence slower?
4. If larger wheels are lighter than smaller wheels (previous owner spent a lot of money on them), maybe faster as car is lighter overall?
4. No difference?
5. Can only tell by carrying out some measured testing,,, but this would be a pain as car is now very much setup for 19" wheels with all suspension geometry all set up.

I would appreciate some advice...

Many thanks
Graham

Acceleration would be affected if the rolling radius of the wheel altered (effectively gearing) or the moment of inertia of the wheel altered, i.e. how hard it is to accelerate about the axle - the greater the mass and distance of that mass from the axis, the harder it is to accelerate the wheel. Suspension would be affected by a greater undamped mass (if the wheels are heavier) and reduced sidewall compliance in the tyres, so you may end up with a less consistent contact patch (even if it is a bit larger) than you would by running smaller rims. In reality it probably matters a lot if you're racing and not that much on the road unless it's unpleasant to drive the car.

I like the look of these wheels on your car. Am I a traditionalist? Well only in as much as I think things need to look like they were designed to be there.

Steve.

[Graham_Amika]

Hi Graham, you didnt buy that car from a guy called Stephen did you? Had his own timber business?

Yes thats the fella, seemed very nice to deal with. Lots of provenance with the car etc.

How do you know him?

[scooterscot]

The suspension was originaly designed for 16 inch wheels the cosmetic look from bigger wheels in most peoples eyes improves the car but in handling terms it has quite a depremental effect.The larger lower profile tyre has a much reduced slip angle which in turn makes the car much less progressive in the transition from full grip to loss of grip,you will also notice a big increase in tramlining when you hit white lines ect.The car will also be slower off the line as it will not have the flex in the sidewalls which helps with contact patch and weight transfere to the back.The real test is on the track 18s are about 4 seconds slower round Knockhill.The car is much smoother in terms of comfort and handling on 16s.

[mxi933]

Graham_Amika said:

Car is in with SSCC now, for a number of niggles, but funnily enough that panel looks OK and appears to be fixed down correctly. It seems the panel might just be a little bit warped but it isn't a problem.

cheers
Graham

Hi Graham - its good to have another Cerb showing up in West Yorkshire.
Just as a matter of interest who are SSCC, where are they and do you reckon they are a decent outfit?

[Graham_Amika]

mxi933 said:

Graham_Amika said:

Car is in with SSCC now, for a number of niggles, but funnily enough that panel looks OK and appears to be fixed down correctly. It seems the panel might just be a little bit warped but it isn't a problem.

cheers
Graham

Hi Graham - its good to have another Cerb showing up in West Yorkshire.
Just as a matter of interest who are SSCC, where are they and do you reckon they are a decent outfit?

I'll let you know in due course. Steve was the head of engineering at HHC as far as I understand it. He was also involved in developing GAZ shocks which is why he is fitting them.

SSCC (Borough Bridge) Jct 37 or 38 off A1... (Specialist and Sports Car Company).

I'll post an update when I get the car back..

[work-shy-wanabe]

I went from 19" aftermarket wheels on Friday to some 18" Spiders. Car feels a lot better. I think its due to the profile increase. It also feels like I should be able to get away with adjusting the damping to a slightly harder setting.

scooterscot said:

less progressive in the transition from full grip to loss of grip

Thats exactly what Ive been trying to improve since purchasing my Cerbera. When I first got it the suspension damping was set to very hard and it had 19" wheels with 30 profile tyres on the rears. So far, some suspension adjustment and fitting some spiders have improved things a lot and Im twice as confident in the car now as it doesn’t suddenly let go anymore. Which used to result in tree views through the front windscreen all the time.


Those 19" do look nice though!

Edited by work-shy-wanabe on Tuesday 8th May 19:37

[MackemPete]

Graham_Amika said:

Hi Graham, you didnt buy that car from a guy called Stephen did you? Had his own timber business?

Yes thats the fella, seemed very nice to deal with. Lots of provenance with the car etc.

How do you know him?

I bought his old spiders off him when he put those alloys on. He certainly looked after that car you could have eaten off his garage floor

[southendpier]

scooterscot said:

The real test is on the track 18s are about 4 seconds slower round Knockhill.The car is much smoother in terms of comfort and handling on 16s.

really 4 seconds, that's interesting. jeepers that's an age! did you experience this?