Different F/R wheel/tire sizing
- Thread starter lumbercis
- Start date
b00staholic
New member
Anybody make a hubcentric 7.5mm or 8mm spacers for the front?
b00staholic
New member
H&R makes 8mm spacers in 5x100, but they won't be hubcentric and the longer studs that come with it won't work on our cars.
http://www.namotorsports.net/detail.cfm ... HR16255571
http://www.namotorsports.net/detail.cfm ... HR16255571
I measured the stock track and posted it up a while ago. The rear is 20mm a side shorter i.e. 40mm total.
At the last autocross I did I took two different pairs of tyres. One was a 225/45 R16 Formula R and the other was a 225/50 R16 Proxy 888. The two different brands are similar in compound and I have measured them to be as close to equal in terms of lap times as possible on a different vehicle. It was wet on the day and the track was quite tight. I noticed that having the smaller rolling diameter on the front pushed less and the measured times where quicker. My car has close to stock alignment with only the rear toe reduced.
So measured fact is that if you want to reduce understeer you need to run a front tyre with a smaller diameter or vise versa.
The rest of what I have to say is based on testing from other vehicles.
If you make something stiffer you are in effect reducing the grip at that end of the car. You are doing this by placing a higher load on that set of tyres and if you look at a tyre slip angle plot you will notice that the relationship between horizontal and lateral load is not linear.
Making something stiffer is not always the best answer. You can soften the other end of the car to acheive the same result. I beleive that for autocross type work the stock spring rates are quite good. I would like to stiffen the rear sway bar a bit, soften the front sway bar as well as place a bit more camber and caster into the front. I have already got rid of a lot of rear toe in. I would not touch the springs and dampers until I measured what was going on when things are clser to optmium. Just a note; if the car is doing something only on corner enry or exit and not mid corner then the most likely problem is the dampers. Making small changes based on factual results is the key
Generally a wider rear track will give more rear grip. This will increase understeer but will also increase drive out of a corner. If you can make the car handle nuteral with a wider rear track then it is going to be faster as you will be able to get out of a corner better. You may find that as a result of changes you make to acheive this that you start to kill the rear tyres. I can not see this being a problem on the GT4.
The quote from whiteline about our cars being like a fwd refers to the lightness and design of the suspension and drive system in the rear. They suggest that it is common for bushes to be worn and they recommend they be replaced. This is quite true.
A smaller steering wheel will not change the angle input required. It will only change the distance movement required to acheive that angle input. The problem of having to cross your hands over will not change.
Roger
At the last autocross I did I took two different pairs of tyres. One was a 225/45 R16 Formula R and the other was a 225/50 R16 Proxy 888. The two different brands are similar in compound and I have measured them to be as close to equal in terms of lap times as possible on a different vehicle. It was wet on the day and the track was quite tight. I noticed that having the smaller rolling diameter on the front pushed less and the measured times where quicker. My car has close to stock alignment with only the rear toe reduced.
So measured fact is that if you want to reduce understeer you need to run a front tyre with a smaller diameter or vise versa.
The rest of what I have to say is based on testing from other vehicles.
If you make something stiffer you are in effect reducing the grip at that end of the car. You are doing this by placing a higher load on that set of tyres and if you look at a tyre slip angle plot you will notice that the relationship between horizontal and lateral load is not linear.
Making something stiffer is not always the best answer. You can soften the other end of the car to acheive the same result. I beleive that for autocross type work the stock spring rates are quite good. I would like to stiffen the rear sway bar a bit, soften the front sway bar as well as place a bit more camber and caster into the front. I have already got rid of a lot of rear toe in. I would not touch the springs and dampers until I measured what was going on when things are clser to optmium. Just a note; if the car is doing something only on corner enry or exit and not mid corner then the most likely problem is the dampers. Making small changes based on factual results is the key
Generally a wider rear track will give more rear grip. This will increase understeer but will also increase drive out of a corner. If you can make the car handle nuteral with a wider rear track then it is going to be faster as you will be able to get out of a corner better. You may find that as a result of changes you make to acheive this that you start to kill the rear tyres. I can not see this being a problem on the GT4.
The quote from whiteline about our cars being like a fwd refers to the lightness and design of the suspension and drive system in the rear. They suggest that it is common for bushes to be worn and they recommend they be replaced. This is quite true.
A smaller steering wheel will not change the angle input required. It will only change the distance movement required to acheive that angle input. The problem of having to cross your hands over will not change.
Roger
Intresting thread with much to think about. Another way to make the rear end more "lively" would be to use a trick employed in Time Attack cars in Japan. Does anyone remember the Bozz Speed EVO in SCC a few years back? I believe the front rims were 16x8, the rears 16x7. The same size tire was used frt.& rear. Not sure about spring rates. Smaller rear rims gave tire a more rounded profile & quicker breakaway/less understeer with supposedly less drivetrain wear & tear that unequal tire sizes might give. Might be worth a shot in autox,
on street maybe not so much.
on street maybe not so much.
CMS-GT4
Active member
I wish we could get Bill to give us input on his tire setup, but he seems secretive about it.
He runs a larger rear dia. on racing slicks during autox. He gave us tires specs sometime ago but he does not post on here much. I think he might be the same guy driing Pat's alltrac for the SCC thing. If that happens anyway.
He runs a larger rear dia. on racing slicks during autox. He gave us tires specs sometime ago but he does not post on here much. I think he might be the same guy driing Pat's alltrac for the SCC thing. If that happens anyway.
abraxxa":3s55ickl said:
yeah, the difference between F and R is almost the same as in the case of ST185...
what are the track specs of ST165?
edit: I've found the specs...
ST165: F track - 1465mm, R - 1440
btw, Abraxxa, are you sure about the ST205 track specs?
cause according to my sources (
) they're: 1510mm (F) and 1490mm (R) :shrug:bridge47":vf30hpfi said:
Are you sure? If the tire has a more rounded profile, it should give a more progressive breakaway - it should have more give, than the front tire which would be more stretched and thus more rigid and prone to breakaway sooner..
Maybe I'm not recalling it correctly - I have that that issue collecting dust somewhere, I'll have to dig it up and take a look at it again..
Either way, its another way of tweaking the handling.
CMS-GT4
Active member
Yes. I have played around with different tire pressure. I alway ran more in the rear so the rear gave a little quicker. Not a whole lot for daily driver. Maybe 32 F and 34 R. I think maybe even higher in the rear for an autox, but I don't think I would advise it for daily driving.
yes, that's what it's for.smog7":1ffe56hs said:
mark d'addio runs crazy wide tires for the front on his evo than the rear for autocross. i forgot the exact width, you can find it on the web i'm sure. he's a multiple-time SCCA solo2 champion. wide tires in front = less understeer.
i'm keeping tabs on this thread. i want to know if it's possible to make the AT behave a bit more like a RWD car at corner entry/mid-corner. because it's definitely FWD-like in those areas. corner exit feels neutral/RWD-ish, so I'm cool with that.
Grave dig
So what do people want from their GT4/Alltracs in terms of handling?
For my car i have always been chasing front end grip on the track, the understeer has always been horrendous.
I kept changing little bits at a time to remove it, and thus far everything has worked, it was progressively getting rid of the understeer.
However at my last track day i got the shock of HUGE oversteer on corner entry and mid corner, once the power was on the AWD did its work and settled it right down.
My setup (as best i know)
Front:
7kg/mm front spring (390lb/in)
-1*45" camber
1*56" caster (yes more)
0mm toe
poly bushes on the front end (minus swaybar oddly enough)
235/40/17 tyres on 17x8+35 wheels
Rear:
4.5kg/mm springs (250lb/in)
-0*45" camber
2mm toe in
Whiteline swaybar on full stiff (too much, have since put it to the middle)
poly bushes on the inner end of the control arms
stock diff mount
stock bushes for control arms (not for lack of trying, couldn't get them undone!)
235/40/17 tyres on 17x8+10 wheels (effectively, 25mm spacer each side)
Additional info:
No meaningful weight reduction at all, battery still in stock location.
I have a custom undertray on the front of the car, extremely doubt it makes a difference to lift/downforce on the front however.
The caster was achieved by rotating camber adjustable strut tops.
I have camber bolts on all 4 corners to get the camber spot on.
The oversteer was insane, it was waaayyyy too much, hence i have softened the rear swaybar.
My apex speeds were some 5-10km/h quicker than the previous setup, could get on the throttle harder and earlier.
I finally managed to get oversteer, so now i am going the opposite way and trying to gain some rear end grip.
After that, i need more power!
So what do people want from their GT4/Alltracs in terms of handling?
For my car i have always been chasing front end grip on the track, the understeer has always been horrendous.
I kept changing little bits at a time to remove it, and thus far everything has worked, it was progressively getting rid of the understeer.
However at my last track day i got the shock of HUGE oversteer on corner entry and mid corner, once the power was on the AWD did its work and settled it right down.
My setup (as best i know)
Front:
7kg/mm front spring (390lb/in)
-1*45" camber
1*56" caster (yes more)
0mm toe
poly bushes on the front end (minus swaybar oddly enough)
235/40/17 tyres on 17x8+35 wheels
Rear:
4.5kg/mm springs (250lb/in)
-0*45" camber
2mm toe in
Whiteline swaybar on full stiff (too much, have since put it to the middle)
poly bushes on the inner end of the control arms
stock diff mount
stock bushes for control arms (not for lack of trying, couldn't get them undone!)
235/40/17 tyres on 17x8+10 wheels (effectively, 25mm spacer each side)
Additional info:
No meaningful weight reduction at all, battery still in stock location.
I have a custom undertray on the front of the car, extremely doubt it makes a difference to lift/downforce on the front however.
The caster was achieved by rotating camber adjustable strut tops.
I have camber bolts on all 4 corners to get the camber spot on.
The oversteer was insane, it was waaayyyy too much, hence i have softened the rear swaybar.
My apex speeds were some 5-10km/h quicker than the previous setup, could get on the throttle harder and earlier.
I finally managed to get oversteer, so now i am going the opposite way and trying to gain some rear end grip.
After that, i need more power!
I would REALLY appreciate seeing some pics of the rotated camber adjustable strut top.
I don't comprehend how you rotated that strut top but maintained 1.45 degrees of camber.
I am close to your setup now and looking to get rid of just a little more understeer.
I appreciate your post. Thank you.
See if you can also post that setup on the correct thread for others.
I don't comprehend how you rotated that strut top but maintained 1.45 degrees of camber.
I am close to your setup now and looking to get rid of just a little more understeer.
I appreciate your post. Thank you.
See if you can also post that setup on the correct thread for others.