Effect of smaller wheels

[Guest]

Hi

 

I have 16" wheels on my Roadsport SV but need new tyres. When I bought the car from Caterham, they suggested smaller wheels might be the first upgrade I consider. Having checked tyre prices, smaller wheels/tyres may be a good option now. K

 

Apart from a readjustment of the speedo ( ), would there be any more significant changes needed if I went to 14" wheels? The car has a LSD.

 

Thanks

 

Jon

[Mort]

Depends upon what size tyres you have now, and what you fit to the 14" wheels. If you have a similar rolling radius then you may not even have to adjust the speedo. There's a calculator here that does the math for you.

 

A larger profile tyre will give a much more forgiving and less harsh ride, and a smaller wheel should also be lighter, so definite benefits to be had.

[Jonathan Kay]

What do you intend to use the 7 for: road, touring, track days, racing... ?

 

Clam shells or cycle wings?

 

Thoughts so far on tyres?

 

What ground clearance do you want?

 

I'd put speedometer accuracy well down in the list of importance: you can always add marks to the dial if you don't want to spend any money on that. But what sort do you have?

 

Jonathan

 

Edited by - Jonathan Kay on 17 Jul 2014 10:50:23

[MacP]

I used to have 16 inch HPC wheels on my 21.

 

I ran 14 inch wheels (K&N Minators)for a while and now have 15 inch wheels. I went back to 15 inches because tyre choice in 14 inches is very limited (and I needed V rated tyres for my 21 which don't exist in sensible rubber).

 

Caterham supplied 14 inch wheels with 185/60R14 Avon ZV3s which are not great tyres for a 7. You can't get Avon CR500s in 14 inch and the only good road tyre IMO is the A021R (185/60R14 diameter 579mm). The 14 inch wheels aren't any lighter than Caterham's 15 inch wheels either. I wouldn't put 14 inch wheels on it because of the tyre choice issue.

 

You could get close to your existing rolling radius of 205/45R16 (diameter 589mm on Toyo T1R) with 185/55R15 (diameter 584mm). On Caterham 15 inch wheels you would save c. 2kg a corner of wheel and tyre weight vs. 16 inch HPCs (which is a lot).

 

13 inch wheels would be the best for weight (= performance) and tyre choice but you would need to run 70 profile tyres on the road to get close to your existing rolling radius. Yoko 185/70R13 A021Rs (diameter 589mm) are good on the road and track (in wet and dry). They are also cheap because they are supplied in bulk as a racing wet by George Polley (see Tyre prices).

 

On paper these have exactly the same rolling radius as the original 205/45R16 set up so you wouldn't need to adjust anything else. You could run 60 profile on the track (diameter 557mm). If you went for less tall tyres you might need to adjust the ride height to avoid grounding, which would require adjustable platforms.

 

If your Roadsport has an electronic speedo you can adjust easily by changing the codes using the black button on the screen.

 

I'd suggest you go for 13 inches and 70 profile. It would be the highest performance wheel choice and I suspect the ride would feel like an S-class Benz after the 16 inch wheels.

 

Edited by - MacP on 17 Jul 2014 11:43:01

[Andy Wendler]

I changed from 16 to 13 with CR500, not had the car long so all new to me, but it has transformed it. Lot less weight (lost the spare off the car as well), acceleration greatly improved and handling 110% better.Having done a track day with both sizes,they are like chalk & cheese, really happy (same cannot be said about my now smaller bank balance!) Cheers Andy

[DougBaker]

I changed from the 16" wheels to 13" with 185/70 tyres recently on my SV.

 

The change in tyre circumference is negligible so no change required to the speedo. I had been worried that the new wheels would look too small on the SV but with the 70 profile tyres I think it improved the look of the car.

 

Not yet had a chance to take the car on track or drive it quickly as I live in Surrey so cannot comment on the change of feel, apart from not having noticed as many pot holes since the change. I also don't care if I have lost a little grip as on track the fun bit is the gentle drifting through the corners rather than the absolute speed you are travelling in my view.

[Guest]

I'm also thinking of changing wheels/tyres.

 

Currently have 6x14 KN Minator wheels on my SV with 185x60 Avon ZV1 rubber (which have no date stamp and I think may be the original road tyres from 2001!).

 

I want to go to A021R's (road use only) but because of the 185x60 cost I am thinking of going to 13" wheels with 185x70 instead...

 

Or am I just being stupid? Am I going to end up paying out loads for new wheels with little or no real benefit? Perhaps I should settle for new 185x60 A021's on the same wheels?

 

HELP!

[Mort]

How about getting 13" wheels for use with A021Rs during the Summer, and fitting the 14" wheels with Winter tyres at a later date?

[rgrigsby]

I've not done a back to back comparison on a Caterham by a friend switched his Westfield from 15" to 13" wheels and the difference was amazing, the ride was better and the whole car felt more alive.

 

As has already been mentioned the usual option is the 185/70 Yoko 21's, you can pick up a second hand set of minilites for £150 so it doesn't have to cost a lot to change.

[Mavic82]

The advantage of 13" wheels is the inertia and mass. However IMHO the current trend of low profile tyres on 13" rims looks wrong. The car was never intended for that combination when originally designed. Originally 13" wheels had very deep section side walls which was not advantageous for performance.

 

Originally the 13, 14, 15 and 16 all had roughly the same rolling radius when fitted with tyres.

 

I have run 16 inch rims for 11 years as I far prefer the look of them. I don't subscribe to the handling benefits of smaller wheels ( bar mass and inertia comment above) the low profile tyre generally associated with larger rim sizes are a vast improvement. But the car does need to be set up differently. In general most Caterhams are to stiffly sprung and with 16 in particular the road springs need to be compliant. Then you get a compliant car with plenty of grip and feedback that has no issue on track keeping pace with smaller wheeled cars. In essence the suspension has to work instead of using the tyre sidewall.

 

I am now just changing to 15" split rims to address the mass and inertia issues. Yes the feeling is better in terms of steering feedback (less white lining) but the tyres are a bit more squishy and I don't like that, it adds a vagueness but it is the best compromise I can put together. I would never go for a smaller rim size.

 

Don't use wheels and tyres to tune ride and handling, choose an appropriate size for you and set the car up around it.

 

Guy

 

Edited by - Mavic82 on 19 Jul 2014 13:33:48

 

Edited by - Mavic82 on 19 Jul 2014 13:36:10

[Guest]

Lots of useful advice here - thanks.

 

Any ideas where I should look for some 2nd hand minilites (other than these forums)?

 

 

[Smithy7]

I agree with the majority and go with 13", not only for rotational mass reasons but the 13's will give you a greater option with tyres.

 

I don't think it'll make much difference to the speedo and it'd be easy to check with a sat nav.

 

Not checked but you should be able to get a set of wheels off eBay.

 

Dave

[Guest]

All

 

Very many thanks for all the advice - it is clearly a bit of a minefield and takes a little while, an lots of web-reading to get your head around the topic. I am thinking of doing some sprinting with the club, probably next year now but with a taster at Curborough in August. I think the conclusion seems to be 13" for the acceleration so I will look around for some offers. I may well keep the 16" given the later comments on balance etc.

 

Jon

[SLR No.77]

On my previous car (1998 - 2007), I had both 13" Minilites (185/60) and 16" HPC wheels and swapped as my mood changed, I always felt the 16" looked better and they certainly had a phenomenal level of grip. However ... I could drive much quicker and safer on the 13's because the handling really shone through and the breakaway point of grip came predictably, unlike the 16's which just let go The car tracks better on 13's and goes pretty well where it's told, 16's tend to have a bit of a mind of their own and the extra rotational mass is quite noticeable.

 

The absolute best handling wheelset I ever fitted was 13"x6" front and 13"x7" rear, running 185 & 215 Yoko 32R's, unfortunately no longer available.

 

My current car runs 13" and I'd never even consider anything else, they simply are the best size for a Caterham and have the best choice of tyres suitable for the low weight of the car. Anyone suggesting that 16" are in the same league is just in denial 😬

 

Stu.

[Guest]

I currently run 13" wheels with 185/60 AO48's. I'm thinking of fitting 15" CSR wheels and CR500 tyres. The overal radius will be very similar and as the CR500 tyres are meant to be much lighter than the Yokos, I can't see much overall difference to rolling mass. Or am I missing something?

[Jonathan Kay]

Easy to measure weight (and derive mass)... has anyone measured rotational inertia?

 

Here's a customised calculator.

 

Jonathan

[robert green]

Does anyone have an idea of how the 15" Prisoner wheels compare weight wise with some of the more modern alternatives, and of course a 13" minilite style wheel?

 

I like the look of them, and have no complants with the way my car handles, but have no comparison and am wondering if I am missing out!

 

 

[MacP]

Quoting Davies-Johnston: 

All

 

Very many thanks for all the advice - it is clearly a bit of a minefield and takes a little while, an lots of web-reading to get your head around the topic. I am thinking of doing some sprinting with the club, probably next year now but with a taster at Curborough in August. I think the conclusion seems to be 13" for the acceleration so I will look around for some offers. I may well keep the 16" given the later comments on balance etc.

 

Jon

 

It's not really a minefield, lighter 13 inch wheels are objectively better.

 

Better acceleration:

Effects of rotational inertia

 

Lower unsprung weight improves handling (this article is off topic but explains the reason why vividly): Hidden evil of unsprung weight

 

Tyres are heavier than wheels. Despite the lower profile, 205/45R16 tyres are actually slightly heavier than higher profile tyres of the same diameter on smaller wheels. So bigger wheels definitely = more weight. HPCs with tyres weigh 15.5kg. HPC wheel and tyre weight 4kg a corner heavier than a 5kg 13 inch wheel with CR500s.

 

The benefit of lower profile tyres is supposed to be reduced sidewall flex. But even on heavy cars it doesn't seem to offer material benefits after c. 55 profile: Effect of lower profile tyres and larger wheels

 

The idea that lower profile = better is Broscience: Myth 5 low profile

 

The one good reason for bigger wheels is to fit bigger brakes. Caterhams don't need bigger brakes.

 

Caterham is running R300s on 175/55R13.

 

The only "reason" left to go with 16 inch wheels would be if you thought it looked better. Which is a debateable point of view. Would a Ferrari 250 GT be improved by "plus-sizing" the wheels with some 19 inchers instead of the Borranis? 250 GT prior to plus-sizing?

[MacP]

Quoting Robert Green: 

Does anyone have an idea of how the 15" Prisoner wheels compare weight wise with some of the more modern alternatives, and of course a 13" minilite style wheel?

 

I like the look of them, and have no complants with the way my car handles, but have no comparison and am wondering if I am missing out!

 

 

 

7kg (about the same as the 16 inch HPC):

Prisoner wheel weight

 

13 inch wheels are generally around 5kg or a bit less. Minators were c. 5.5 kg.

[robert green]

Thanks!