Andy135 Posted November 10, 2022 Share Posted November 10, 2022 I have a new to me Sigma Superlight on the way, which is currently on 15 inch 10 spoke anthracite wheels and CR500's (2007 vintage if I remember correctly, which seem too old to be safe). I've read the threads on here and PH regarding 13's vs 15's but what's not clear to me is whether for Sigma cars 6 or 8 inch rears are preferred. Any suggestions or opinions either way?Next question would be on rubber. What are the current preferred tyres for a car that will be 80/20 road/track? Link to comment Share on other sites More sharing options...
Jonathan Kay Posted November 10, 2022 Share Posted November 10, 2022 On width: how much power will that be? There's a crossover point that's often suggested.ThanksJonathan Link to comment Share on other sites More sharing options...
Andy135 Posted November 10, 2022 Author Share Posted November 10, 2022 It's a fixed cam 150. Link to comment Share on other sites More sharing options...
ptr_drvr Posted November 10, 2022 Share Posted November 10, 2022 I haven't any other experience, but I run 13 x 8" rears on a Sigma 140 with ZZRs. Never lacking in grip, that's for sure. Link to comment Share on other sites More sharing options...
David_Stamp Posted November 10, 2022 Share Posted November 10, 2022 I run 13" Apollo staggered (6" ZZS on front + 8" ZZS on rear) on a Sigma Roadsport 150 SV.Others have said that 6" front and 6" rear are 'adequate', but I didn't get my Caterham to be 'adequate'...[Check if you need to change your front cycle wings because of the change in wheel diameter from 15" down to 13". I have seen others say that this might be a problem. I moved from 14" wheels to 13" wheels which avoided this issue] Link to comment Share on other sites More sharing options...
StevehS3 Posted November 10, 2022 Share Posted November 10, 2022 I have had both. Handling: I think I prefer 6" front and rear. Looks: I prefer wider rears particularly as I like a slightly higher ride height and they fill the arches better. Link to comment Share on other sites More sharing options...
Area Representative DerekH Posted November 10, 2022 Area Representative Share Posted November 10, 2022 I'm also running 13" Apollo's with 6" fronts and 8" on the rear on a 270S sat on ZZS's. 8" and 215's on the rear just look better.Recommend you get it flat floored and the ride height adjusted to suit the 13" wheels. Ride height on the front drops significantly going from 15 -13Best change I've made to my car!DerekH Link to comment Share on other sites More sharing options...
7 wonders of the world Posted November 10, 2022 Share Posted November 10, 2022 185/205 Toyo R888R on 6"/8" will offer a light more by way of ground clearance, excellent tyre too. Link to comment Share on other sites More sharing options...
Area Representative Golf Juliet Tango Posted November 10, 2022 Area Representative Share Posted November 10, 2022 2007 vintage if I remember correctly, which seem too old to be safeFar too old, replace as soon as you can. Link to comment Share on other sites More sharing options...
Andy135 Posted November 11, 2022 Author Share Posted November 11, 2022 #9: I quite agree.As for the 6's vs 8's debate, I'd prefer predictable, readable handling, and from what I've read 6's on the rears are better for this than 8's. Does this bear out for those of you who run 6's? I love the look of the wider 8's but would prioritize handling if there's a difference to be had. Link to comment Share on other sites More sharing options...
aerobod - near CYYC Posted November 11, 2022 Share Posted November 11, 2022 I run 15x6.5 wheels with 195/50-15 tyres all around for general touring purposes and 13x6 with 185/60-13 front and 13x8 with 235/45-13 rear tyres for blat or track use.There is definitely more tail-out action with the narrower rear tyres, the wider ones obviously give better grip out of tight corners, but shift the tail-out action to a higher speed. The handling is just as good and predictable with either set.The narrower set win out in the wet due to higher road pressure leading to less wheel spin on anything wetter than just a damp surface. Link to comment Share on other sites More sharing options...
Andy135 Posted November 11, 2022 Author Share Posted November 11, 2022 #11, thank you - that is just the sort of insight I was hoping for. Link to comment Share on other sites More sharing options...
Phil G Posted November 12, 2022 Share Posted November 12, 2022 I assume the speedo will require recalibration if the rolling radius changes. Link to comment Share on other sites More sharing options...
aerobod - near CYYC Posted November 12, 2022 Share Posted November 12, 2022 Hi Phil,It does need recalibrating if you want the most accurate reading, but with the electronic Caerbont speedos is easy to do. I used to swap backwards and forwards, but now just calibrate for the larger diameter wheels (576mm for the 195/50-15 tyres, 542mm for the 235/45-13 tyres), leaving the 6% difference when on track or blat on the 13" wheels, as I swap wheels at least a dozen times each driving season.Swapping the suspension settings for the different tyre sizes (mainly due to slight rake change with the 13" staggered wheels in my case) is more of a challenge, but I keep mine optimised on the 13" wheels and accept a bit of a compromise on the 15" wheels. Link to comment Share on other sites More sharing options...
Phil G Posted November 12, 2022 Share Posted November 12, 2022 #14 Yep, just pointing out to thread originator. Link to comment Share on other sites More sharing options...
Jonathan Kay Posted November 12, 2022 Share Posted November 12, 2022 "I assume the speedo will require recalibration if the rolling radius changes."Yes, and the ease of doing that depends on the type of speedometer.Jonathan Link to comment Share on other sites More sharing options...
John Vine Posted November 12, 2022 Share Posted November 12, 2022 #14: For info on how to recalibrate a Caerbont programmable speedo, see Part C of this Guide.JV Link to comment Share on other sites More sharing options...
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