KRL Posted October 6, 2012 Share Posted October 6, 2012 When I purchased my 125 Sigma it came it came with 8 inch R13 wheels and is fitted with CR500s all round. I am starting to wonder whether I should down size these to 6 inch on the rear. Therefore I would like to know the general consensus of opinion on here - Benefits of downsizing vs the cons and and the benefits of sticking with what I've got vs the cons. Should also add that my car has got Wide Track front suspension, would this have any bearing? Also has an open diff. Link to comment Share on other sites More sharing options...
keybaud Posted October 6, 2012 Share Posted October 6, 2012 You can fit different width tyres on a wheel, but there will be changes to the handling, due to the change in sidewall angle. I have 7 inch rears with 205 tyres, but the wheel will take 185 to 225, I believe. What tyre width do you have now and why do you think you need to change? Note that changing the width will also change the ride height, so you may want to look at which profile you need too. Link to comment Share on other sites More sharing options...
KRL Posted October 6, 2012 Author Share Posted October 6, 2012 I have 205 width CR500s on the rear at the moment. The profile on CR500s is 55 for both 175 which I have on the fronts and 205s which I have on the rear so I don't think ride hight should change if I changed to 175 CR500s on the rear. Why do I think I should change? - 6 inch wheels would be lighter. I also get the feeling 8 inch wheels on the rear might be overkill on a 125 BHP car. Edited by - KRL on 6 Oct 2012 13:58:40 Link to comment Share on other sites More sharing options...
diggerman Posted October 6, 2012 Share Posted October 6, 2012 I've just fitted 8in 205 x R13 rear and 185 x R13 front to my Roadsport 150 SV. Tyres are yoko 044. I wondered whether it my be inclined to under steer but in fact the handling is really good and the car looks great! Peter Link to comment Share on other sites More sharing options...
Ged Posted October 6, 2012 Share Posted October 6, 2012 Quoting KRL: I have 205 width CR500s on the rear at the moment. The profile on CR500s is 55 for both 175 which I have on the fronts and 205s which I have on the rear so I don't think ride hight should change if I changed to 175 CR500s on the rear. Why do I think I should change? - 6 inch wheels would be lighter. I also get the feeling 8 inch wheels on the rear might be overkill on a 125 BHP car. Edited by - KRL on 6 Oct 2012 13:58:40 If you fit 175/55's to the rear you would need to raise the rear ride height by about 16mm to keep it the same as previous. Edited by - Ged on 6 Oct 2012 22:07:14 Link to comment Share on other sites More sharing options...
Drumster Posted October 6, 2012 Share Posted October 6, 2012 The profile represents the height of the sidewall as a percentage on the tyre width, so: sidewall height of 175/55 = 96.25mm sidewall height of 205/55 = 112.75mm Therefore changing to 175 at rear will reduce ground clearance at the rear by 16.5mm and consequently affect the rake of the car. 205s on the rear of a 125bhp car may well 'overtyre' the car. Just for comparison's sake I run 185/75/13s on 6" rims front and rear on my 190bhp car for the road and that still gives you plenty of grip unless you're being too lary..... Link to comment Share on other sites More sharing options...
KRL Posted October 6, 2012 Author Share Posted October 6, 2012 Ah ok thank you as I did not realise the profile was a percentage of the tyre width! So if I change the rear size I will need to re-adjust the rake as well, good to know thanks. I don't really have anything to compare against as this is my first 7 and just wonder if it might be better with 6 inch rears. The Caterham Supersport (140 BHP) comes with 6 inch rears as well I noticed. Link to comment Share on other sites More sharing options...
keybaud Posted October 6, 2012 Share Posted October 6, 2012 Quoting KRL: Ah ok thank you as I did not realise the profile was a percentage of the tyre width! So if I change the rear size I will need to re-adjust the rake as well, good to know thanks. I don't really have anything to compare against as this is my first 7 and just wonder if it might be better with 6 inch rears. The Caterham Supersport (140 BHP) comes with 6 inch rears as well I noticed. I would change them if it doesn't drive properly, but I wouldn't change it just for the sake of it. You can fit 205 tyres on a 6 inch rim, but it's at the limit and the sidewall angle will be a bit wonky. As for the extra weight, if it's that important to you, take off a shirt and don't wear any pants. Link to comment Share on other sites More sharing options...
Boss Hogg Posted October 7, 2012 Share Posted October 7, 2012 I have 6" rears on my 140 Supersport. When I enquired about 8" rears at the time of ordering the car form Caterham i was told that the car would be 'overtyred' with 8" rears. Never driven a car with 8" rears and I don't have any traction problems with mine at the moment . Link to comment Share on other sites More sharing options...
KRL Posted October 7, 2012 Author Share Posted October 7, 2012 I would change them if it doesn't drive properly, but I wouldn't change it just for the sake of it. You can fit 205 tyres on a 6 inch rim, but it's at the limit and the sidewall angle will be a bit wonky. As for the extra weight, if it's that important to you, take off a shirt and don't wear any pants. The car drives well and I want to make it drive better and extract the maximum I can from it so if this helps I will do it! I would not put 205s on 6 inch rears though, I would likely go with 175/55 CR500s all round. Edited by - KRL on 7 Oct 2012 10:52:58 Link to comment Share on other sites More sharing options...
KRL Posted October 7, 2012 Author Share Posted October 7, 2012 I have 6" rears on my 140 Supersport. When I enquired about 8" rears at the time of ordering the car form Caterham i was told that the car would be 'overtyred' with 8" rears. Never driven a car with 8" rears and I don't have any traction problems with mine at the moment . Interesting to know, thanks. So what are the donwsides of overtyring the rear? More understeer maybe? Link to comment Share on other sites More sharing options...
Mankee Posted October 7, 2012 Share Posted October 7, 2012 Where in Suffolk are you? I've got a spare pair of 6J 13" Minilite wheels with tyres (not CR500s though) that you are welcome to try out for a little while to see what you think before making jump. Link to comment Share on other sites More sharing options...
KRL Posted October 8, 2012 Author Share Posted October 8, 2012 PM sent. Link to comment Share on other sites More sharing options...
KRL Posted October 8, 2012 Author Share Posted October 8, 2012 I sent Caterham an email on the same subject and received a reply this morning. Caterham's opinion is that I would benefit from fitting 6 inch wheels to the rear and as a rule of thumb they only fit 8 inch rears to cars with > 160 BHP otherwise it can induce understeer on lower powered cars. Link to comment Share on other sites More sharing options...
Bradders Posted October 8, 2012 Share Posted October 8, 2012 I've got 6" all round on 13" CR500 on a 125 Academy with an open diff. I find it has plenty of grip and only a couple of times has it broken away in the dry, and I was being a litle heavy on the loud pedal tbh. Wet is a different matter of course. Only thing I'd say would be is that 8" do fill the arches nicer, and look a little tougher. That is maybe going down the Max Power route too much possibly Looks aside I'd say CC are right there on the overtyred point, but I'm no expert. Bradders. Link to comment Share on other sites More sharing options...
RedCat7 Posted October 8, 2012 Share Posted October 8, 2012 Has anyone thought about making a pair or narrower rear wings that might improve the look of the 6" wheels? Link to comment Share on other sites More sharing options...
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