Wheel and Tyre Sizes

[Andy Checkley]

There has recently bee lots of good comment on tyres, types, pressures etc, but something that has puzzeled me is why the top end performance sevens like the Superlight R, R500 etc are fitted with 13" wheels and tyres, when most modern high performance cars are fitted with low profile 15", 16" and above? I have heard that it is because of the range of track suitable tyres in the 13" size. Is this the only reason, or are there other handling/performance reason?

 

I apologise in advance if I am asking a silly question.

 

Regards, Andy Checkley

 

 

[Dartmoor7]

7s are much lighter than ordinary cars and need a different type of tyre to work at their best.

[Barry]

Definitely not a silly question.

 

Generally speaking, the 13" wheel and tyre combination will be lighter and therefore the unsprung weight is lower. This is more important with lightweight (comparatively, that is) cars where the ratio of sprung to unsprung is improved by a greater percentage than it would be if you made the same change to your normal tin-top. The lower the unsprung weight, and therefore the better this ratio, the more control the springs and dampers can exert, and consequently, the handling should be better.

 

There is also the issue of gearing; as a rule, the overall gearing of say a 175/70x13 is the same as a 185/60x14 and a 195/50x15. So a 185/60x13 is more lowly geared than a 185/60x14, most of us are willing to sacrifice the cruising ability of a larger wheel/tyre combination in order to achieve maximum revs in top gear.

[Alex Wong1697456877]

13" wheels give so much more feel than the bigger wheels. The feedback from the smaller wheels gives you that much more confidence to play with slip angles and also lowers the gear ratio's - ie more acceleration.

 

Wider wheels will grip more but bigger wheels (diameter) probably don't add to grip and just take away feel.

 

The 7 is so light that the larger sidewall doesn't really detract from the handling. If you we're worried about this, you could try ACB10's which have extremely stiff sidewalls. They are slightly lower profile than Yoko's but the walls feel rigid compared to Yoko's, adding to a kart like feel if that's what you want.

 

Having said all of that, I still think the 16" wheels with flared wings looks fantastic and the knowledge that the tyres will last for ages was also satisfying. Once you go to 13's though, you won't go back!

 

I'm sure there are many out there with more a more scientific explanation!

 

 

 

Alex Wong

alex.wong@lotus7club.co.uk

http://www.alexwong.net

Home : 44-(0)121-440 6972

Fax : 44-(0)121-440 4601

 

Edited by - Alex Wong on 4 Apr 2000 10:57:22

[Slipper man]

In addition to all the above, which I agree with whole-heartedly, there is one other factor that is important in choice of tyre size, which is the rubber compound used. Tyres only work properly when warm, and it takes a certain amount of weight to get a tyre to warm up. Larger wheels tend to be on larger cars, so that even if the tyres look the same, tyres made for smaller (e.g.13") wheels normally use a softer compound than those built for larger wheels.

 

One of the reasons the rubber on larger wheels lasts longer is that on Seven it never gets warmed up. As Alex says - if you ever get 13" wheels on your car, you'll never go back (better grip, better feel, less tramlining, better ride).

 

If you live in the Caterham area you are welcome to try fitting a set of my 13" or 14"

wheels to see what they feel like on your car.

[Graham Perry]

I currently run 13,14 & 15" on my car, and 13" are the best.

[Andy Checkley]

Thanks everyone for your replies, and the offer of a try of some 13" wheels from Keith.

 

I currently run 15" wheels with cycle wings, and so subsequently my car has the larger cycle wings. If I change from 15" to 13" wheels can I just change the cycle wings or do the stays have to be changed also?

 

Also, I noticed a question on the site the other day about changing between 15" and 13" wheels and I thought that there may be an issue with final drive ratios. I maybe incorrect but I believe that the 13" wheeled cars have a 3.62 final drive but the 15" cars have a 3.92 final drive. If this is correct is the difference significant enough to matter? This may be interesting as I sometimes use my car for trackdays, and although I have a six speed box, I rarely use 6th. Retaining a higher final drive ratio with 13" wheels may enable me to make more use of 5th and 6th on the longer straights. Current my car (K VVC)pulls about 6200rpm or there abouts flat out on the Lavant straight at Goodwood, so to save downchanges, I tend to leave the car in fifth when it will pull 7000rpm or so before I have to start breaking for Woodcote.

 

Thanks, Andy

[Steve Brown]

I run 13" wheels with cycle wings for 15/16" wheels. This allows the cycle wings to sit rotated more towards the rear of the car (if you see what I mean) which catches more of the stones and muck that normally gets sprayed using standard cycle wings.

Going back to the earlier discussion regarding wheel size, somebody once mentioned the additional benefit of 13" (lower weight) as having a lower gyroscopic effect than larger (heavier) wheels, therefore improving the ability to change direction quickly.

[Vogon SuperTrooper]

Thanks for the question and the answers. What's a good price for a set of 13 or 14 inch wheels?

Charles

[Charles E-H]

Caterham are currently offering a 13" wheel/tyre package for 120ukp. This is for 6" K&N minilite style rims with Yoko32R tyres. No fitment worries if you have AP brakes.

 

 

[Gary G]

I too have been thinking about switching from 15" to 13", but I have another concern. With smaller wheels, they will spin faster and therefore put more miles on my odometer? Is this right and is there an easy fix?

[Dartmoor7]

It's not the size of the wheel that matters,it's the overall diameter of the wheel/tyre combo.

13" wheels with 185/70 tyres have same as 16" wheels with 205/45.

[Rob Morris]

If you wish to change over your front stays, then I suggest that you contact Terry Bithell (Wales Area Organiser) as he is trying to go in the opposite direction i.e. has got 13" and wishes to fit 16" but has found that his front guards are in the way! One question that I have with changing the wheel dia. is that I have been lead to understand that a smaller wheel may afect the front geometry and would need adjustment? P.S. which tyres are rated as the best for road use Yoko's Avon's ?????? Help required!

[Alex Wong1697456877]

(copied from another thread)

 

For a road Seven, I'd go for 021R's - 185 60 13 all round. If ground clearance is an issue, you can get them in 70 profile. Not very pretty but prettier than a puddle of oil under your car! Alternatively, go for bigger wheels if ground clearance is a problem.

 

If the 021 lifespan (approx 5-7000 miles for pure road use) is too short, I'd go for A520 yoko's but I think they've just replaced them with something newer. I use 14" A520's - 10,000 miles and hardly worn, but they're nowhere near as good as the 021's I had.

 

Other choices? 032R's are good in the dry so if you don't take the 7 out in the rain, these would be ideal. ACB10's aren't great road tyres - short lifespan, lower profile (& rideheight), plus they're expensive.

 

 

Alex Wong

alex.wong@lotus7club.co.uk

http://www.alexwong.net

Home : 44-(0)121-440 6972

Fax : 44-(0)121-440 4601

 

 

Alex Wong

alex.wong@lotus7club.co.uk

http://www.alexwong.net

Home : 44-(0)121-440 6972

Fax : 44-(0)121-440 4601

[V7 SLR]

If you want to play about with gearing, final drive ratios and tyre/wheel diameters, Dave Andrews' web site has a fantastic gear ratios program that is downloadable. It's only a few Kb but has been invaluable to many when choosing gearboxes/ratios, wheel/tyre diameters and diff ratios. Check it out at:

 

http://hometown.aol.com/Dvandrews/index.htm

 

... and click on the gearing program link.

[Ben_S]

So how much should you pay for a set of 4 021Rs and who should you buy them from? (185/60 or 185/70 r13)

 

 

[Andrew Russell]

Best deal that I have managed to find recently was at Demon Tweeks in Wrexham. I was quoted £136 for two 185.60-13 A021R's and that included delivery.

 

Anybody out there cheaper??

[Peter Mears]

Purchased four tyres last year from demon, and they seemed to be cheapest. They deliver them to which is a bonus.

[Andrew Russell]

EARS of Macclesfield, Cheshire also stock A021R's and their prices are very similar to Demon Tweeks, give or take a few coppers.(That's pence to you youngsters!!)

[Graham Sewell]

For Yoko 021R in 185/70R13 try George Polley in Heathfield (01435-863679). AT 40ukp per corner fitted, they are unbeatable. No connection with George other than as a satisfied customer. Also, note these are not old stock, he claims to get through 2000 of these tyres each year!

[Graham Perry]

I have used George Polley as well for Yokohama and they are about the cheapest I have come across. They get through so many AO21Rs as George Polley supply the short circuit Hot rod boys where he made his name as a great racer. Several classes of hot rods use the 21R as a control tyre.

[catse7en]

At present I run my Caterham VVC on standard Prisoner wheels and Michelin 195/50/15

 

I have read the various messages about the benefits of 13" wheelsand must say I have certainly seen how much more effective Yoko 32R's are than Michelin on trackdays.

 

However I live in a very wet area (near Dartmoor) and would want a road tyre that is good in the wet. I am moving towards the idea of Yoko 021R on 13", Now a lot has been said about the 185/60/13. Can anybody comment on which would be the more sensible choice

 

021R in 185/60/13

 

or

 

205/60/13

 

The larger tyre will give me similar diameter - and therefore will keep gearing similar, and therefore the speedo will remain accurate. But would the 205- in gaining similar diameter to 15" loose out on providing the benefits of 13" - reduced unsprung weight etc.

 

Would this overtyre the car? (about 5mm greater tyre widthaccording to Yoko's literature.

 

Now a further query

 

If I move to 13" what wheels?

 

Regards

 

John Gathard

 

Caterham VVC

[Alex Wong1697456877]

I used 021R's 185 60 13 all round on a 200BHP car and it didn't feel undertyred for road use. Even on the track, it was a well balanced setup, if not the ultimate in grip - it was very forgiving and allowed a relative novice like me to push the tail out safely and most importantly, it never did anything suddenly unless you blatently overdid it.

 

205's will give you more tramlining and less feel. I would use 185's at the front. You could put 205's on 6inch rims on the back but I'm not sure you'd get a huge amount of benefit on the road. Having said that, I don't think it would be detremental, especially with the tourque of the VVC to deal with. It would look nicer too - the 185's look so narrow under the rear arches.

 

Wheels - do you have, or intend to ever get the big brake kit? If so, I'd use K&N minotaur wheels as supplied by Caterham. Not all 13" wheels fit over the larger calipers.

 

 

Alex Wong

alex.wong@lotus7club.co.uk

http://www.alexwong.net

Home : 44-(0)121-440 6972

Fax : 44-(0)121-440 4601

 

 

 

Edited by - Alex Wong on 22 Apr 2000 00:12:10

 

Edited by - Alex Wong on 22 Apr 2000 00:13:06