Tyres, handling and performance
Discussion
My 2500M project car is pretty much standard and is at the point where I need to be putting the wheels back on. I have the original(?) Wolfrace wheels... With 185 HRx14 tyres....
How well does the car handle with these tyres on there?
I need to get some new tyres, is it worth getting larger wheels, or do these very high profile tyres actually grip quite well?
What modern tyre combination do people find works?
How well does the car handle with these tyres on there?
I need to get some new tyres, is it worth getting larger wheels, or do these very high profile tyres actually grip quite well?
What modern tyre combination do people find works?
To the best of my knowledge, the last "high performance" tire to be manufactured in the correct aspect ratio for your application was the Michelin XWX. If shod with these, your car would handle quite well by late 1960s and even by early 1970's standards. Tire technology has benefited from almost forty years of continuous development since those days. Although the wolfies are beautiful, you can make dramatic performance gains with the change to low profile / wider tyres. Without body modifications, I had 205 65s on my '75 M. I'll misquote Emerson Fittipaldi here who said that you can make the largest single performance improvement with the smallest amount of money spent by changing the wheel / tire package on your car.
A part of the performance boost comes from the reduction in sidewall compliance. This does contribute to a harsher ride. The ride characteristics of your car will change markedly. See if you can get a ride in an M that has already undergone such a change; that way you will be able to tell if you would appreciate the trade-off.
Have fun,
B.
A part of the performance boost comes from the reduction in sidewall compliance. This does contribute to a harsher ride. The ride characteristics of your car will change markedly. See if you can get a ride in an M that has already undergone such a change; that way you will be able to tell if you would appreciate the trade-off.
Have fun,
B.
1975 M original specification
“T slot” wheel size: 14” x 6”
Offset: ?
Tire size 185 ~80 14
14.43cm + 17.78cm = 32.21cm road to axle CL
Circumference: 202.38cm
Original wheels retained,
tires replaced by
205 65 14
13.33cm + 17.78cm = 31.11 cm road to axle CL
Circumference: 195.47cm
causing a ride height reduction of 1.1cm,
and a 3.5% reduction in top speed (120 mph becomes 116 mph)
New wheel/tire specification as follows:
Wheels:
"Complete Custom Wheel" three piece wheels -polished centers machined from 6000 series forgings w/ polished, spun 5000 series shells
Front....._?_______on 4 1/2"(114.3mm) X 5-bolt w/___?" backspace
Rear.....9 1/2" wide on 4 1/2"(114.3mm) X 4-bolt w/ 4 1/2" backspace
Tires:
Front.......Kumho Exsta Supra 712 235/40 WR18
Rear........Kumho Exsta Supra 712 275/35 WR18
(25.57” Diameter)
(80.35” Circumference) 204.1cm
Hope this helps,
Bernard.
“T slot” wheel size: 14” x 6”
Offset: ?
Tire size 185 ~80 14
14.43cm + 17.78cm = 32.21cm road to axle CL
Circumference: 202.38cm
Original wheels retained,
tires replaced by
205 65 14
13.33cm + 17.78cm = 31.11 cm road to axle CL
Circumference: 195.47cm
causing a ride height reduction of 1.1cm,
and a 3.5% reduction in top speed (120 mph becomes 116 mph)
New wheel/tire specification as follows:
Wheels:
"Complete Custom Wheel" three piece wheels -polished centers machined from 6000 series forgings w/ polished, spun 5000 series shells
Front....._?_______on 4 1/2"(114.3mm) X 5-bolt w/___?" backspace
Rear.....9 1/2" wide on 4 1/2"(114.3mm) X 4-bolt w/ 4 1/2" backspace
Tires:
Front.......Kumho Exsta Supra 712 235/40 WR18
Rear........Kumho Exsta Supra 712 275/35 WR18
(25.57” Diameter)
(80.35” Circumference) 204.1cm
Hope this helps,
Bernard.
That is very very useful information thankyou. I have just been looking at custom wheels, but the price is a bit ouch at the moment...
How much difference to handling etc did fitting the 205 65 14 wheels to the standard rims make?.... Seems an enormous jump from 185 to 205
I don't suppose you have any photos of the car with those tyres fitted do you?
How much difference to handling etc did fitting the 205 65 14 wheels to the standard rims make?.... Seems an enormous jump from 185 to 205
I don't suppose you have any photos of the car with those tyres fitted do you?
Edited by tegwin on Saturday 20th September 19:07
On the 14" wheel, IMHO you are best off with a 185 or 195/70. On these size tyres the car will handle very predictably and progressively. Putting wider tyres on a standard road car IMO does it no favours (except that perhaps you get more choice of rubber). Overtyring a car causes the limit to be higher but the breakaway is much more sudden, the car will be more likely to aquaplane in the wet and unless the rear arches are modified you are likely to kiss them with the tyres on full suspension travel.
Also on wider tyres the tyre is more likely to roll on the rim, as for better performance you are better matching the rim size to the tyre size to prevent flexing in the tyre sidewall.
davidy
Also on wider tyres the tyre is more likely to roll on the rim, as for better performance you are better matching the rim size to the tyre size to prevent flexing in the tyre sidewall.
davidy
Sorry about the incorrect previous info, (senility setting on too soon for comfort) actual tires used were Yokohama 321 195/70/14 and, later, Yokohama AVS VR 195/65/14. I encountered no problems with fouling @ full bump and these tires were within manufacturer's specification for fitment on a 6" rim. My car is equipped with Spax adjustable shock absorbers and (according to my Demon Tweeks bill) the following springs:
Front-14” 225Lbs
Rear-14” 130Lbs
As I asked for a 10% rate increase while maintaining the factory ride height, this does not coordinate with the following info stolen from somewhere on the net.
Factory Specifications For 2500M Springs:
______________________Front________________________Rear_
Free Length____________14 3/4"______________________13 1/4"
ID____________________2.68"_______________________2.26"
OD___________________3.562"______________________3.06"
Mean Dia.______________3.125"______________________2.66"
Rate__________________135 lbs/in___________________140 lbs/in
Gauge________________.437________________________.400
Active Coils_____________12 ¾_______________________13 ¾
Total Coils______________14 ¼_______________________15 ¼
One of the problems with 70 aspect ratio tires is that with the advent of low profile, high-performance tires, manufacturers stopped producing high-performance (grippy) tires. Their agressive compounds as well as the more sporting tread patterns are used on their low-profiles. As far as tires rolling on the rim is concerned, taller sidewalls allow for this to occur more readily, think longer lever.
For maximum performance, get new wheels. My car had a fair bit of space left to add tire width on the (rear) inside even after fitting the wider tires. Of course, this would increase turning radius if you are looking to fit the same tires in the front as the rear.
Whatever you do will be a compromise between cost, performance, comfort and looks.
Good luck.
Front-14” 225Lbs
Rear-14” 130Lbs
As I asked for a 10% rate increase while maintaining the factory ride height, this does not coordinate with the following info stolen from somewhere on the net.
Factory Specifications For 2500M Springs:
______________________Front________________________Rear_
Free Length____________14 3/4"______________________13 1/4"
ID____________________2.68"_______________________2.26"
OD___________________3.562"______________________3.06"
Mean Dia.______________3.125"______________________2.66"
Rate__________________135 lbs/in___________________140 lbs/in
Gauge________________.437________________________.400
Active Coils_____________12 ¾_______________________13 ¾
Total Coils______________14 ¼_______________________15 ¼
One of the problems with 70 aspect ratio tires is that with the advent of low profile, high-performance tires, manufacturers stopped producing high-performance (grippy) tires. Their agressive compounds as well as the more sporting tread patterns are used on their low-profiles. As far as tires rolling on the rim is concerned, taller sidewalls allow for this to occur more readily, think longer lever.
For maximum performance, get new wheels. My car had a fair bit of space left to add tire width on the (rear) inside even after fitting the wider tires. Of course, this would increase turning radius if you are looking to fit the same tires in the front as the rear.
Whatever you do will be a compromise between cost, performance, comfort and looks.
Good luck.
It always amazes me the wealth of knowledge on here...
Slow M... How did the car handle with those springs?.... I dont suppose you have a record of the open/closed length of damper you bought/fitted?
Not quite sure why I am worying over the finer points such as this when the cars wiring loom is in pieces all over my bedroom floor
...but hey ho..
Slow M... How did the car handle with those springs?.... I dont suppose you have a record of the open/closed length of damper you bought/fitted?
Not quite sure why I am worying over the finer points such as this when the cars wiring loom is in pieces all over my bedroom floor
...but hey ho..tegwin said:
How did the car handle with those springs?...
I think the change helped the car lean slightly less in corners and it seemed to improve my confidence. Yes, it did feel faster through turns but it also acquired a harsher ride. I don't have much of a basis for comparison to other cars. Despite having driven a 5000M and a couple of 3000Ms, mine is the only 2500M I have ever driven. It is also the only M series car I have ever truly flogged. tegwin said:
I don’t suppose you have a record of the open/closed length of damper you bought/fitted?
Measured @ bolt CL =17 1/8” fully open. Travel is +- 4 1/4” to rubber bump-stop fitted inside in shock absorber. Front springs have +- 13 coils.
Rear springs have 15 coils.
Bernard.
TVR_owner said:
Bernard,
Do you not find those spring rates a little on the soft side for spirted driving?
John, Do you not find those spring rates a little on the soft side for spirted driving?
I am sensing that the numbers quoted by demon tweeks on these parts may not have been accurate. Unfortunately, there is no expedient way for me to verify the info. I do think there was a great deal of improvement upon installing this spring/shock combination and tossing the originals, which were starting to wear out.
I've posted (see above) what http://www.tvrna.com/tech-m02.html shows as being the factory specifications for 2500M. Do you have a recommendation for more sporting spring rates for these cars?
Adrian@ said:
John, Bernard, my thoughts
IF you use the alloy collets from Spax the preload is nearly an 1" more, and under full compression the rear collets clash with chassis lugs giving metal to metal contact....Just my thoughts (from memory, I think the collets are marked up 73M)
Adrian@
Adrian, IF you use the alloy collets from Spax the preload is nearly an 1" more, and under full compression the rear collets clash with chassis lugs giving metal to metal contact....Just my thoughts (from memory, I think the collets are marked up 73M)
Adrian@
congratulations, my senility is worse than your senility!
The collets are indeed marked M73. Also, yes, the rear lugs were clearanced slightly to avoid contact. Oh, and the installed length of the springs with those collets is 12".
This would indicate that -prior to installation on the car, the preload @ each front corner =270Lb and @ rear corner =440Lb.
Bernard.
Edited by Slow M on Thursday 25th September 16:23
Bernard,
I belive our 3000S runs close to 300lb fronts and 225 rears and it's not too stiff.
My race car (no good for road use), 800 fronts and 400 rears.
The S drives very well but still rolls in corners - down to a standard front ARB I belive.
The race car runs 26 mm front ARB and no roll (helped no doubt by the springs!)
I belive our 3000S runs close to 300lb fronts and 225 rears and it's not too stiff.
My race car (no good for road use), 800 fronts and 400 rears.
The S drives very well but still rolls in corners - down to a standard front ARB I belive.
The race car runs 26 mm front ARB and no roll (helped no doubt by the springs!)
My Taimar ran similar spring rates to TVR_owner's S Turbo, complete with a slightler thicker ARB. Yes it rolled but not excessively though.
You should be wary of going too hard at the rear for several reasons: traction in the wet being the main one (potential oversteer!) but you also run the danger of damaging one of the alloy uprights on our lovely pot-holed roads. TVR_owner can obviously go a lot stiffer on his race car as circits are smooth, unless you get some evil exit curbs, but I'm sure that John will stay away from them!
In my experience the biggest handling difference came when Adrian corner-weighted the car, after that it was just superb on road and track
davidy
You should be wary of going too hard at the rear for several reasons: traction in the wet being the main one (potential oversteer!) but you also run the danger of damaging one of the alloy uprights on our lovely pot-holed roads. TVR_owner can obviously go a lot stiffer on his race car as circits are smooth, unless you get some evil exit curbs, but I'm sure that John will stay away from them!
In my experience the biggest handling difference came when Adrian corner-weighted the car, after that it was just superb on road and track
davidy
tegwin said:
It always amazes me the wealth of knowledge on here...
Duncan, I'm with you on this! Adrian@ said:
...a lot of really good stuff...
TVR_owner said:
...a lot of really good stuff...[/
DavidY said:
...a lot of really good stuff...
Adrian, John, David,
you guys are awesome! Thanks so much for the GREAT info.
Bernard
Edited by Slow M on Saturday 27th September 17:03
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