SteveP Posted August 27, 2002 Share Posted August 27, 2002 I have searched the archives for this one, and it has been done to death, but still find myself confused as to what I need to order and from where. I have a 1989 De-Dion xflow (135bhp increasing to around 160 soon I hope) currently running 6.5 x 15 Prisoner wheels (plus rubbish 195/50 tyres) and want to make the change to 6 x 13" KN Minator with 185/60 Bridgestone RE720 (has to be list 1A for sprints) So questions: 1) What offset do I need front and rear to ensure no rubbing and correct track? 2) Previous posts have suggested a reduction in ride height of 25mm or so. I have adjustable platforms so I am assuming that this reduction could be compensated for by appropriate tweaks? Has the reduction caused anyone any issues? 3) Can people who have made the switch describe the tangible results - I noticed at Curb that almost everyone had 13" rims so there must be something in it 4) Where can I get this wheel / tyre combo from? Polley Motorsport seems favourite, but any others? 5) What will the approximate weight saving be do you think? Thanks SteveP Link to comment Share on other sites More sharing options...
Jaseb Posted August 27, 2002 Share Posted August 27, 2002 I'm up for this too (since yesterday), my other question is how is the speedo affected?! And would me 7 ultimately end up being slower at top end but quicker getting there on smaller diameter tyres and by how much? I've the prisoners too. Link to comment Share on other sites More sharing options...
scooby dooby doo Posted August 27, 2002 Share Posted August 27, 2002 1 offset is i think 18mm. Rob M is the expert though... 2 you can work out the ride height difference from the tyre size (assuming that the numbers on the tyre are correct...) radius of the tyre is: half the wheel diameter + profile/100 * width ie 195/50R15 are: 15"/2 + 195 x 50 / 100 = 190.5 + 97 = 288 mm ie 185/70R13 are: 13"/2 + 185 x 70 / 100 = 165.1 + 129.5 = 294 mm ie 185/60R13 are: 13"/2 + 185 x 70 / 100 = 165.1 + 111.0 = 276 mm so the difference is pretty small and you'll gain with 70 profiles 3) i've never tried 15" wheels but yes, the change is apparentally HUGE 4) polley will do it. other people make lighter wheels though. 5) how much will you spend on wheels? i don't know how heavy prisoner wheels are. also from new to worn out a tyre looses nearly 1kg of rubber.... borrow a wheel and RE720 in the relevant sizes and stick iton the bathrom scales... HOOPY CYCLE WINGS CUCUMBER Link to comment Share on other sites More sharing options...
Violet Elizabeth Posted August 27, 2002 Share Posted August 27, 2002 2) With 70 profile A021's there is no noticable difference in ride height 3) The difference is very noticable, less tramlining, slightly more forgiving ride , but the first time you get them on track.... wow ! 4) For an easy life it is very difficult to better Polleys, although technically possible to get wheel tyre combos cheaper, the difference is minimal and the service is excellent. 4) Think someone did a wheel/tire weight comparision a while back ? Have a browse of the archives. As a recent 15" Michelin to 13" Yoko convert all I can say is Just Do It Link to comment Share on other sites More sharing options...
Jaseb Posted August 27, 2002 Share Posted August 27, 2002 ta much gents. time to shop 😬 Link to comment Share on other sites More sharing options...
murph7355 Posted August 27, 2002 Share Posted August 27, 2002 To back up what the others have said: 1) Just ask for deDion Caterham ones. I think they're Ford fitment and the std. offsets on 6" rims will work fine for the widths you're talking. 2) No issues at all, even with 60 profile tyres. I only came down from 14" wheels but as Hoopy pointed out, there's so little difference it's not worth fussing over. Adjustable platforms will be able to compensate for it if you have adjustment left. But you're better off with the car lower anyway (just be vigilant over speed bumps - but you have to do that anyway). 3) Switching from 14 to 13 the biggest difference I noticed was how quickly the car turned in. Really darted to the intended point much more sharply and felt much more precise. Note, however, that this could have been due to rubber. 13s give you much more scope for much better rubber. So there's another advantage. Rubber is cheaper. There's another. And subjectively the handling feels much more composed and controlled. Which I've put down to less weight being hurled around. But this will no doubt differ depending on suspension set up etc. Biggest advantages are (a) less weight, (b) less cost for reshodding and © better rubber available. 4) Go to Polley. Good prices and you get tyres and wheels at the same time. He'll also know what to sell you if you ask for Caterham deDion wheels! 5) Weights are on the site somewhere. I think the design of wheel you're looking at will come in between 4.5kg and 5kg. I'd be surprised if the 15" wasn't more in the range 6kg-7kg but could be wrong. On top of that the tyres are likely to be lighter (as they're smaller) which could be enhanced further by going for ACB10s or CR500s (different construction so even lighter - don't think these are 1a tyres though). You could well be up for saving anywhere between 2kg and 5kg per corner. And it's all where you need to save weight (unsprung mass so the suspension can concentrate on controlling the car rather than your wheels). Key thing - just do it Don't think I know of anyone who went 13"s and got rid of them because they didn't think it was an improvement. andy@c7consulting.com Link to comment Share on other sites More sharing options...
Steve Robinson Posted August 27, 2002 Share Posted August 27, 2002 Ah Jason, the search for speed has begun already has it.... this is going to cost us a fortune by May next year, as predicted yesterday !! Now where's that number for Ratrace to get the new superlight flat floored..... Robbo Link to comment Share on other sites More sharing options...
DohNut Posted August 27, 2002 Share Posted August 27, 2002 A small word of warning on the early DeDeon tubes. I brought some freshly refurbished rims from this very site and put them on my 1988 DeDeon, Front were fine but at the back the *Heel* of the tube caught the rim of the wheel requiring a 5mm spacer (3mm may have been enough). I mentioned refurbished because the machining had removed the manufacturers name from the rim so this may not be a prob with other combinations of wheel manufacturer and / or design of DeDeon tube. Nick Link to comment Share on other sites More sharing options...
Jaseb Posted August 27, 2002 Share Posted August 27, 2002 Steve Everything will be fine, trust me- I have Jane's credit card..... Now I'm sure I read about caron fibre clamshells somewhere In my head I've spent 2 grand and counting 😬 Link to comment Share on other sites More sharing options...
eric Posted August 27, 2002 Share Posted August 27, 2002 Hello, me too I have 1989 Caterham I found the car perfect with 195/50 15 Yoko A539 and very cheap to replace (when old but not dead) a friend of mine has 021R yoko with 13" wheels and he will buy 15" wheels because, 021R are used in less Than 4000 miles and are expensive to replace (compare to the A539) A539 good in the wet and also in the dry (much more better than the Michelin pilots) regards Link to comment Share on other sites More sharing options...
Violet Elizabeth Posted August 27, 2002 Share Posted August 27, 2002 70 profile A021s are about the same price as A539s. Yes, they wear out quicker, but they are stickier. Swings/roundabouts etc Anything is better than Pilots 😬 Link to comment Share on other sites More sharing options...
scooby dooby doo Posted August 27, 2002 Share Posted August 27, 2002 wearing out 021Rs in 4000 is pretty extreme.... OTOH - my last set of 32Rs only lasted 1600 miles including 4 trackdays 😬 😬 😬 😬 HOOPY CYCLE WINGS CUCUMBER Link to comment Share on other sites More sharing options...
F355GTS Posted August 27, 2002 Share Posted August 27, 2002 I believe the standard Caterham offset is 23mm Mark Link to comment Share on other sites More sharing options...
scooby dooby doo Posted August 27, 2002 Share Posted August 27, 2002 i think 23mm is for 7" wheels and 18mm for 6". or is it the other way around.... 🤔 HOOPY CYCLE WINGS CUCUMBER Link to comment Share on other sites More sharing options...
Jaseb Posted August 27, 2002 Share Posted August 27, 2002 Well I seem to be left in a mild dilemma I've got to the point where I think I have a couple of options, I can have: 1. Yoko AO21's 185/70's all round with 6" minataurs for 425 notes delivered OR 2. Yoko AO32's 185/60 with a 6" rim on the front and 205/60's on a 7" rim on the back for 546 notes delivered. Whadya reckon anyone? Is the extra wedge worth it. I'm kinda keen to keep the same ride height if poss, same rolling radius and hence same top speed if poss(concious of the faster tracks and certainly not wanting to go any slower down the straights ) and not to have my speedo to far out. I think these tyres will be kept mainly for the track and the odd hooly thru milton keynes. Then of course there's brake upgrade to go inside them but I'll leave that for another day 😬 Link to comment Share on other sites More sharing options...
scooby dooby doo Posted August 27, 2002 Share Posted August 27, 2002 the speedo is normally miles out anyway. don't let it cloud your decision ❗ HOOPY CYCLE WINGS CUCUMBER Link to comment Share on other sites More sharing options...
Steve Robinson Posted August 27, 2002 Share Posted August 27, 2002 Jase, FWIW I'd go for the A032's. I put them on my first superlight and they totally transformed the way it felt, loads of grip and looked the utter bo****ks 😬 Let's face it what's another 100 quid in the total scheme of things !! Robbo Link to comment Share on other sites More sharing options...
murph7355 Posted August 27, 2002 Share Posted August 27, 2002 How much power have you got? It's impossible to put an exact figure to the cutover point, but I reckon 185s all round are a good set up for something around the 160-180bhp mark (and anything below). Over that and 205s on the back work well. If you put too much tyre on the back it'll unbalance the handling and be hard to get the back to slip nicely. Too little and you'll spin a lot of power away no matter what LSD you have. You can fit 185s to 7" rims so if you wanted flexibility later and don't need a spare, go with 6" fr and 7" rr. If you use your car predominantly on the road, get 21Rs. They last longer than 32Rs and on the road there's barely any perceptible difference in outright grip. Conversely there's a marked difference in wet weather (the 21Rs being better). And 21Rs are by no means a dead loss on the track. The mix of 185/205 tyres you noted in 21R flavour will cost about the same as the 32Rs (excluding the fact they'd last twice as long). 32Rs do look nicer. But they wouldn't look too cool wrapped round a lamp post if you misjudged it in the rain! Link to comment Share on other sites More sharing options...
scooby dooby doo Posted August 27, 2002 Share Posted August 27, 2002 i wouldn't press the wet weather element too much. in standing water a seven isn't very good and you'd be a fool to push it - saying thast - the 21 will be better in thewse conditions. if the surface is greasy or damp the 32 will be better because its softer rubber. anyway - just take it easy in the wet and get the best tyre (in your opinion - given costs/wear etc - for the dry). FWIW I've had GREAT fun on wet/damp/drying tracks with 21s and 32s. both tell you what they're doing until they aquaplane in deep puddles. HOOPY CYCLE WINGS CUCUMBER Link to comment Share on other sites More sharing options...
scooby dooby doo Posted August 27, 2002 Share Posted August 27, 2002 i wouldn't press the wet weather element too much. in standing water a seven isn't very good and you'd be a fool to push it - saying thast - the 21 will be better in thewse conditions. if the surface is greasy or damp the 32 will be better because its softer rubber. anyway - just take it easy in the wet and get the best tyre (in your opinion - given costs/wear etc - for the dry). FWIW I've had GREAT fun on wet/damp/drying tracks with 21s and 32s. both tell you what they're doing until they aquaplane in deep puddles. HOOPY CYCLE WINGS CUCUMBER Link to comment Share on other sites More sharing options...
Jaseb Posted August 27, 2002 Share Posted August 27, 2002 Well power is as supersprint (135) at present(!) the thing I was conerned about is current gearing on 15's gives 115mph-ish top whack, anything smaller (and I do like the AO32 185/60 sketch a lot don'tget me wrong) and I thought I may stugggle into 3 figures? I'll more than likely use the 15's regularly on the road, with yoko AVS they're pretty good and use the tiddly wheels when it really counts I'm talking myself into option 1 I think, either way I think it'll be enough to keep out of (or should that be in?) mischief for a little while at least. Link to comment Share on other sites More sharing options...
murph7355 Posted August 27, 2002 Share Posted August 27, 2002 If you use 70 profile tyres you may lengthen your gearing...? Tyres are very subjective but I personally have never found 32Rs better than 21Rs in damp or wet conditions. And you can feel 21Rs cutting through water where 32Rs just aquaplaned on my car. Soft rubbers not much use to you when it's separated from the road by water... Not pushing it too hard is very good advice though! FWIW CR500s seem equally adept in the wet after sampling them in a torrential downpour on Saturday. But in the first 750 miles or so they don't seem worth twice the price of 21Rs. andy@c7consulting.com Link to comment Share on other sites More sharing options...
Drumster Posted August 27, 2002 Share Posted August 27, 2002 Jase, I was in the same position as you running a supersprint on 15" prisoners and Michelin Pilots. I decided to go for 13" supalites with 185/70/13 21Rs and have never looked back. My reasoning was that the new wheel tyre combo gave the same ride height and gearing and the 21Rs in 70 profile are only £40 inc VAT from George Polley. The difference in handling became very apparent very quickly. The 7 is used predominantly on the road but I do manage about 3/4 trackdays a year. I reckon on about 6,000 miles from my 21Rs. Chris Alston 1800 Supersprint - Loud and Proud 😬 ...well it only sounds fast officer 😳 Brooklands aeroscreens for that real open top motoring feeling Link to comment Share on other sites More sharing options...
NickD Posted August 27, 2002 Share Posted August 27, 2002 Just to reiterate Doh!Nut's warning, the rear hubs on early de Dion cars (up to 91?) were the std Ford drum brake hub. Later cars had Caterhams own hub which increased the track by about 5mm per side. The use of the early hubs can allow some 13" wheels (supalites) to foul the end of the deDion tube. Easily resolved by the use of spacers or a bit of gentle grinding on the end of the deDion tube. The early Ford hubs have large (about 1" dia) lightening holes between the studs so are easily identified. Link to comment Share on other sites More sharing options...
scooby dooby doo Posted August 27, 2002 Share Posted August 27, 2002 you say your current gearibng gives 115 mph. fit 70 profile 13" tyres and it'll be geared for a bit more... HOOPY CYCLE WINGS CUCUMBER Link to comment Share on other sites More sharing options...
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