I ran rear 205/60/13 Yokohama in the day and I still run a front 185/60/13.

I use 225/45 ZR13 Hankook on 8" wheels all round,rear guards are slightly pumped and inner guards relieved

I thought that I would keep this thread going rather than hijack Simon's IPRA Nationals thread as I have a number of questions to ask based on what has been written in that thread.
Following the ride height specs Tom has kindly given us I went about and did my best to get the SSS close to that. Given that my Kumho tyres appear to be around 9mm taller than Toms Hoosiers it was always going to be an uphill battle but I did get it fairly close, The upshot of that was after driving it 300 metres down the road and back it has just about ruined the top outer edge of the right rear tyre. The swaybar has hit the exhaust as it goes over the diff and the swaybar itself had to be disconnected to even drive out the garage as the links were seriously binding up as well as the arms hitting the diff tubes. All in all not a happening thing so the absolute best that I can get the back down to would be 135mm as measured from the body join below the sill ( allow another - 4.5mm for the tyre diameter difference between Toms Hoosiers and my Kumhos ) so that would make if roughly equivalent to 130mm. The front down to 125mm.
Given that the last race meeting I came away rather unhappy with the lap times and overall handling of the car and had it reported back to me that even though on the exit of the corners the car appeared to be sitting flat mid corner through the apex it was like 'a double decker bus'!
I had grand hopes that dropping it may have gone a long way towards curing this but to be honest any more than a 10mm drop and I will be playing with fire as far as rear guard clearance goes.
The thing that really puzzles me when I am driving it the car itself does not feel overall too bad and I can't really say yes its pushing terribly here or its loose as here- it just is not precise in the corners and does not seem to be carrying enough exit speed relative to other cars ( including a 1200 coupe that up to the last meeting have always had the edge on )
I had grand hopes that dropping it down may have gone a long way towards getting that mid corner body roll better but thats off the table now as I do not want to start massaging guards given the historic nature of the car.
This then raises the question what else can be done to limit that mid corner roll?
Harry made a comment to Simon re front RC being too high- is this because he had lifted his pick up points in the crossmember by 25mm or is it because of the 45mm roll center spacers?
Just to refresh my setup is 275lb front springs on adjustable B110 struts with Koni inserts, 20mm 3 position adjustable front bar ( currently set in the middle setting )approx 30mm roll center spacers, a whisker under 4 degrees negative camber and 4 degrees positive caster, 2mm toe out.
Rear is a beefed up copy of the John Taylor springs- interestingly still with a very small amount of curve in them, Group 2 Escort Bilsteins and an adjustable 16mm bar.
I haven't measured my track ( do you guys do it from inner to inner? ) but it is definitely wider in the front than the rear.
Are the roll center spacers a good thing? To be honest when I put them in I do not notice any difference whatsoever.
And just to add some more confusion given that my 2 main tracks are predominantly left hand corners and one in particular is renowned for give the right front tyre absolute hell the tyre wear is really good- nice and even across both the front tyres.
Would really appreciate some knowledgeable input here as I am really struggling on this one.
Cheers
Dave

Quote:

Yes, Track is the width measured at the tire centerlines and is wider at rear

I remeasured the front & rear because after rereading Simon's thread the measurements I gave for my car seemed to be off. From the body join the car is now 140mm rear and 125 mm front. The 120/110 was pre-H190 and pre 25mm RC spacers. I raised the rear shackle mounting point so it was level with the front, previously the rear mount was slightly higher than the front shackle mount.

The Addco rear bar attaches as follows; the bushings are bolted up to the frame rail via u bolts (installation required drilling two holes down trough the rails accessed by removing rear side panels) the ends of the bar via a special clamp that allows the use of a standard link. Where the bar itself travels across the car and goes over the diff just above the flange.

As for tires I have previously tried Avon bias ply, I think they were ACB9s, these didn't have the ultimate stick that the Hoosiers do but offered more clearance. I think they were 6.0 x 13. They are taller than the Hoosiers and the side wall has a bit of wind up but are super super predictable, I could hang back out like a Scandinavian rally star. I don't have an apples to apples comparison with the Hooisers as the Avons were takes offs. New Hoosiers were 3 seconds faster but there is a 2 second gap between old and new Hoosiers. My guess is the slightly narrower Avons are 3/4-1 second slower.

I do have one observation about the mid corner lean angle; when the tires start to go off on my car it starts to feeling like it is stalling mid corner especially when it comes to rapid direction changes. It's like it's tripping over the outside front tire. Even though I've stopped winding on steering, the car continues to compress/roll for a split second. If you've ever made the mistake of getting on the marbles with the outside edge of the tires it's a similar feeling to that. I likely won't explain this correctly but my driver attempting to be an eni-gi-near is that as I aggressively turn in on tires that are now 99.5% that the tires are actually washing across the road. They are only "washing" across the road say 50mm and I'm only losing 3-4 hundredths but over the course of 18 to 22 corners it adds up to 1/2 to 3/4 of a second per lap.

The Hoosier tires will do 10 to 12 heat cycles before they go off; there is a spot on my local track that's a 150 degree right into a 45 degree left into a set of 3 - 30 degree lefts. The 3 left handers done correctly form a triple apex left, with fresh tires the 45 left into the 3-30 left can be taken flat but around heat cycle 9 or 10 I may have to breath the throttle back to say 15/16ths for a nano second or sometimes I won't have to lift but I see a tiny dust cloud in the mirror due to rear tire hang maybe 15mm of tire tread of the track edge. 3 or 4 heat cycles after this it's clear the tires are going as I am now lifting back to 1/2 throttle for 5ft or so just after turning into the 3-30 left.

If the car is on rails for a few laps then goes off I'd look around to see if there is a tire that will last a whole session or maybe modify the set up to take the edge off and keep,the tires even f the whole session. Better to start out say 1/2 to 3/4 of second slower on the first laps to keep,the tires from falling of 2-3 seconds a lap. On my 125 GP bike you could go somewhere between .5 to .8 faster on the first 3-4 laps but then about 1/2 way round lap the next lap they'd start to get greasy. You,just had to ride use them 99.8% and be mindful about really aggressive inputs.

Tom

Thanks Tom, that puts my mind at ease a bit re ride height but I am still going to pursue dropping it down to roughly your original heights.
I've had a good talk to my mechanic and taken some measurements and I am going to get the diff housing re bent to 1 degree negative camber. At present it has just under half a degree and after measuring the front wheels which are 4 degrees negative, from the bottom edge to the top edge of the mag is a difference of 28mm so divide that by 4 equals 7mm per degree.
There is already a 3mm difference between the bottom and top edges of the rear mag which lines up with the half odd degree of negative that has already been pressed into the diff housing.
So assuming I have got this about right there should be a gain of 4mm with the extra negative and I have just had an engineer friend of mine look at the mag and he's comfortable that he can safely remove 5-6mm from the inside so that combined should give me around 10mm of extra clearance which should do the trick.
Interestingly when looking at the right rear tyre the inside quarter is clearly not really doing much so some more negative should help there. (does seem a bit odd but again if the car is leaning over...)
I will also have to remount a new rear sway bar most probably coming off the spring platforms but I think that all this should be relatively easy.
If that doesn't help it then I give up!
Re the tyres going off- the rears were new and definitley did not seem to offer as much grip as the worn ones that came off.Most people that I have spoken to here talk of the Kuhmos lasting a season with ease if rotated and they generally get better as the tread starts dissappearing.
You would'nt be able to post a picture of the Addco bar by any chance? I'm just trying to get my head around how that all fits up.
Cheers
Dave