skydragon Posted September 22, 2009 Share Posted September 22, 2009 In anticipation of competing in class 3 next year and my local club allowing usage of list 1b in their Road modified classes, I wonder if those running Kumho ecsta v700 tyres can please help me with the following questions; 1) I'm going to buy a set of Compomotive CXR wheels. I believe the Khumo 215's need a 8" rim? although a 7" rim is acceptable. Any views on 7" or 8"? 2) Currently I'm considering the CXR1380 wheel (see here but am unsure what offset is needed for this style of wheel (it has a recessed centre hub). Any ideas? 3) Supersoft, soft or medium compound? 4) Will these wheels/tyres fit under a standard CC cycle wingstay? If not, what do I need to adjust/alter on the stays? I'm looking to use the wide cycle wings as sold by Fluke here (in GRP) Link to comment Share on other sites More sharing options...
robmar Posted September 22, 2009 Share Posted September 22, 2009 1) - I run them on 7.5 fronts but cannot see why 7's wouldn't fit , at the rear can't see there being toomuch difference but happily to be proved wrong 2) - sorry no idea 3) - if it is for competing them either the S or SS, I think the difference between the 2 is marginal, bu they are the same cost 4) - possibly depending what you have I guess, you may at keast want wider arches to cover the tyres Link to comment Share on other sites More sharing options...
Matthew Willoughby Posted September 22, 2009 Share Posted September 22, 2009 Chris, I can't help on the tyre questions I'm afraid (I have stuck 175/60 Kumhos on my new car) but having met you at Harewood I look forward to seeing and competing with you at more L7C meetings next year Link to comment Share on other sites More sharing options...
Area Representative Richard Price Posted September 22, 2009 Area Representative Share Posted September 22, 2009 Chris, I'm going to use 7.5" MB's all around (with 5" inners and 2.5" outers, work out at ET6.35). Offsets are a bit of an issue. Standard Caterham offsets at 8" are quite inset, but these won't fit on the front without significant spacers. If you wish to use 7.5" wheels without spacers, then they need to be around ET6, but if you went upto 8" then they would need to be more like ET0. If you were to try the tyres on 7's, then because the tyre will bow out more, then you'd need an offset more like ET10. Compounds - ar Rob says (but I'm going to use SS) 215's will fit under standard wings, but the wing needs to have notches cut in the sides so that they can be fitted further over to cover the tyre. Link to comment Share on other sites More sharing options...
Simon.Rogers1 Posted September 22, 2009 Share Posted September 22, 2009 Chris Not sure what offsets you need but I can give you the rim sizes we use (never have understood the "offset" term but that could be as I've not read about it fully. As rob states most of us run a 7.5 inch front wheel with the 215 on them. This is made up from 5 inch inner rim and 2.5 inch outer. This maintains the standard inner dimension from the 6.5 inch wheel widths we were previously using thus saving on cost and allowing the wing stay to be retained. The preferable method of covering this width of tyre is with the CSR style wing and new stays. These are available from either Freestyle or 7 Tweeks. Both have slightly different set ups but both work well. As for dropping to 7 inch width I would only say I have seen the tyre on a 6.5 rim and it does not look correct. The side wall is pinched to tight in my opinion. However that 1/2 inch could make all the difference The rears will be good at 8". We have a 6" inner and 2.5" outer. Compound. The super soft seem to be lasting well on the fronts and there does not seem much difference however I am reliably informed that if the weather this year had been warm enough at our events then we would have experienced a significant difference. We just have not got them fully up to temp this year. IMHO. BUT just to stop you there, I do not think there are any Super softs available at present. There were 40 tyres delivered this year and they have all gone. Of course the best person to ask about availability is Mel Williams on 07811 269500 Link to comment Share on other sites More sharing options...
Simon.Rogers1 Posted September 22, 2009 Share Posted September 22, 2009 Must type quicker. Looks like you have beaten me again this year Richard 😔 Link to comment Share on other sites More sharing options...
mikes Posted September 22, 2009 Share Posted September 22, 2009 In case it is any help - the super softs have lasted pretty well for a whole year's sprinting - that includes Llandow and Pembrey - possibly the most severe tests. Doubt they will last another year though! Not sure how much of an advantage they were and it felt that they were probably going off on the second lap at Llandow - but by then you are pushing much harder. having said that, for the same price, and assuming they were available , I would go for them again. You never know, they may justy give you an edge 😬 Mike Link to comment Share on other sites More sharing options...
mikes Posted September 22, 2009 Share Posted September 22, 2009 Oh, and just to say I used 7.5" wheels from Image - I got the cheaper 2 piece ones using the offset etc that worked for Shaun - they have been fine, and were just as quick, or quicker than those mag ones on other 7s in Class 3 😬 😬 Mike Link to comment Share on other sites More sharing options...
Support Team Shaun_E Posted September 22, 2009 Support Team Share Posted September 22, 2009 I was considering using Compomotive CXRs but couldn't seem to find the right offset. The fronts were the main problem. In the end I gave up and bought some Image 3 piece wheels. I just asked Image to build them with the same backdepth as the Caterham wheels (i.e. they just stick out further). If you blatmail me, I'll send you a copy of the order form. I have 7.5" front and 8.5" rear. You could call Compomotive and see if they can match the Caterham backdepth in 7" or 8" wheels. I think Paul Forster is running CXRs but he has flared wings so won't have the clearance issues with cycle wingstays. Yellow SL #32 - member of Drowned Rat Racing Link to comment Share on other sites More sharing options...
skydragon Posted September 23, 2009 Author Share Posted September 23, 2009 Thanks for all the advice guys, much appreciated. but having met you at Harewood I look forward to seeing and competing with you at more L7C meetings next year Thanks Matthew, likewise, me too. (I managed to beat the 70 second barrier at Harewood last week with a 69.75, so objective achieved for this year, as a newbie!!). Hope the new car is going well. I gave Compomotive a call and they are going to email me some typical 8" rim offsets they have supplied for Caterham's (ET20 ish I think...). But to be sure I am going to measure one of my existing rims, work out the offset and then get a wheel made with an offset that makes the wheel stick further out, so there is no new inwards movement and as such it then doesn't foul the wingstay on the inner. (as Shaun says). The chap from Compomotive advised the 1381 wheel (as opposed to the 1380 which I preffered the cosmetic look of) as it has far better caliper/brake clearance potential. If you blatmail me, I'll send you a copy of the order form. I have 7.5" front and 8.5" rear. Blatmail sent Link to comment Share on other sites More sharing options...
skydragon Posted September 23, 2009 Author Share Posted September 23, 2009 Some useful info from Compomotive Example of Caterham CXR wheels Front wheel - CXR1370 7x13 overall wheel width 200mm. Offset et18. Wheel backspace 118mm. Outboard measurement 82mm approx. Rear wheel - CXR1381 8x13 . Overall wheel width 225mm. Offset et24. Wheel backspace 137mm. Outboard measurement 88mm approx. Wheel backspace measurement taken from wheel mounting face to outer edge of inner rim. Wheel outboard measurement taken from wheel mounting face to outer edge of outer rim. Would advise using the CXR1381 casting if planning future ‘big’ brake upgrade as does offer a little more clearance than the deeper dished CXR1380. So looking at using a 8" rim on the front - Although 137mm backspace is ok for the rear wheel (with ET24), It won't be OK for the front, as doing a forum search reveals that the front backspace should be around 113mm. Lets go with the 118mm front backspace Compomotive state. This would mean with a 8" rim, 137mm minus 118mm = 19mm that the wheel needs to move outwards by, which would mean the offset on the front wheel would need to be ET43. The 1381 wheel is available in offsets up to ET46 so this should be all OK. I'd rather have a set of four identical wheels/rims, but on a seven, with this info above, it's seems like this isn't possible and that I need different rims for the front and back. If I tried to run ET43 all round, this would mean the rear wheels would also have a 118mm backspace....but I think this would make the wheels stand proud of the rear wheel arches. Conversely if I went for ET24 all round (137mm backspace), the rears would be ok, but the inner edge of the front wheels would be approx 24mm further out from the existing wing stays. Do my sums and reckoning ring true???? Edited by - skydragon on 23 Sep 2009 13:17:59 Link to comment Share on other sites More sharing options...
Area Representative Richard Price Posted September 23, 2009 Area Representative Share Posted September 23, 2009 Do my sums and reckoning ring true???? I've not go the time to work it through, but, No. ET43 sounds all wrong. that would be VERY inset. As I said, MB's with 5" inners and 2.5" outers work out at ET6.35. that is inset by 6.35mm Link to comment Share on other sites More sharing options...
skydragon Posted September 23, 2009 Author Share Posted September 23, 2009 ahhhh I think I've added rather than subtracted the required offset.... 😬 Time to do my sums again.... Thanks Richard. Link to comment Share on other sites More sharing options...
skydragon Posted September 23, 2009 Author Share Posted September 23, 2009 Speaking with Kumho motorsport today the 215/50 r13 can use a 7" - 8" rim, with 8" being optimum. (as an aside, I also discovered that the ecsta V70a is the same tyre as the ecsta V700 and a tyre ordered as a V70a will have V700 on the sidewall, both are one and the same and are list 1b). With this in mind I'm probably going to go with; Fronts - CXR1370 7x13 overall wheel width 200mm. Offset et15. Wheel backspace 115mm Rears - CXR1381 8x13 . Overall wheel width 225mm. Offset et27. Wheel backspace 140mm All fiited with Kumho escta v700 215/50 r13, probably in soft compound. Edited by - skydragon on 23 Sep 2009 16:54:00 Link to comment Share on other sites More sharing options...
4ster Posted September 23, 2009 Share Posted September 23, 2009 Chris You seem to have reached a conclusion so I don’t want to confuse things for you but…….! I use Kumhos with CXR wheels and find that the 215s fit the 7” & 8” rims equally well. I have a small preference for 8” on the rear but it is marginal – or maybe I’m just not sensitive enough! The potentially confusing bit is in the offset. My car is a live (English) axle,so may not be representative, but ET 24 on a 7” will fit either end. The 8” are ET 19 of the "later” style, giving extra clearance for the calliper. It all works for me Paul Link to comment Share on other sites More sharing options...
Support Team Shaun_E Posted September 23, 2009 Support Team Share Posted September 23, 2009 Chris - you will be very close to the wingstay with your proposal for the front but it should work. If too close it can easily be solved I suspect by bending the stay. Let us know how you get on as it is certainly a cheaper option than MB or Image. Yellow SL #32 - member of Drowned Rat Racing Link to comment Share on other sites More sharing options...
skydragon Posted September 23, 2009 Author Share Posted September 23, 2009 Chris - you will be very close to the wingstay with your proposal for the front I've just gone into the garage and measured one of my spare 6" rim r13 minilites, as is currently fitted to the car. The wheel backspace is 110mm and the tyre sidewall (185/60 r13) bulges out by approx 7mm beyond the wheel rim edge. On the car there is a 10mm gap between the tyre sidewall and the existing wingstay. 10mm sounds like a sensible gap to retain, so if we presume the 215's will bulge out by approx 7mm when fitted on a 7" rim, then I will need to preserve a 110mm wheel backspace (ie. 115mm backspace would only leave a 5mm gap) so it looks like the fronts will have to be; Fronts - CXR1370 7x13 overall wheel width 200mm. Offset et10. Wheel backspace 110mm This ties in with the 111mm wheel backspace your wheels were ordered with Shaun Edited by - skydragon on 23 Sep 2009 21:40:00 Link to comment Share on other sites More sharing options...
Adrian Williams Posted September 24, 2009 Share Posted September 24, 2009 I think your presumption that the 215 will bulge by 7mm on a 7" rim could cause you a problem. A 215 actualy measures closer to 225 and as Simon pointed out earlier will bulge on a 7" rim, 7mm isn't much of a bulge. Most of us run them on 7.5" rims but if I was you I'd find someone who uses a 7" and get them to measure the bulge before you get some new wheels. Adrian Link to comment Share on other sites More sharing options...
skydragon Posted September 24, 2009 Author Share Posted September 24, 2009 I'd find someone who uses a 7" and get them to measure the bulge before you get some new wheels Anyone with 215 tyres on a 7" rim able to measure the bulge of the sidewall over the wheel rim? Link to comment Share on other sites More sharing options...
4ster Posted September 24, 2009 Share Posted September 24, 2009 Just measured the "bulge" (steel rule across tyre - distance to edge of rim) on mine: 215 on 7" CXR - 6.5mm either side 215 on 8" CXR - Level with rim. I hope that this helps. Paul Link to comment Share on other sites More sharing options...
skydragon Posted September 24, 2009 Author Share Posted September 24, 2009 Top Dollar !! *thumbup* Thanks for doing that so promptly Paul. This confirms that a 110mm wheel backspace will be OK for the fronts, using a 215 on a 7" rim. Link to comment Share on other sites More sharing options...
Chris101 Posted September 24, 2009 Share Posted September 24, 2009 Paul, You really should get out more 😬 😬 😬 Fixed those brakes yet, mind you don't really need them at Anglesey C&L If only everything in life was as simple as a 7!! Link to comment Share on other sites More sharing options...
4ster Posted September 24, 2009 Share Posted September 24, 2009 C&L Working at home today - garage door only a few feet away & I'm easily distracted! Another brake mod. coming up for Anglesey. Bit of an experiment so I had better re-fit the trowel bracket. Hoping to give you some serious competition this time but who knows? Paul Link to comment Share on other sites More sharing options...
Mark Durrant Posted September 24, 2009 Share Posted September 24, 2009 Another brake mod. coming up for Anglesey I'll be there and look forward to seeing it in action .....from a safe distance 😬 😬 Link to comment Share on other sites More sharing options...
Adrian Williams Posted September 24, 2009 Share Posted September 24, 2009 Skydragon Guess of 7mm vs 6.5mm actual. For goodness sake man you were 0.5mm out, get your act together 😬 😬 Adrian Link to comment Share on other sites More sharing options...
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