Handling effects fitting of wider tyres.
Discussion
I am trying to get my head around the effects of fitting wider tyres. What seems simple is really rather complex.
The effect of going too wide seems to be that it could cause the tyre to suddenly let go when weight is transferred away from the tyre.
Has anyone fitted wider tyres and noticed an increased tendency to suddenly let go? If so, what sizes were fitted?
I have found quite a bit about increased grip with lower, wider tyres, but less about the traction. I have found that the standard rears are rapidly wearing and prone to wheelspin since the engine gained horses.
The car is nicely balanced at the moment on standard wheels, but I am changing to 17” wheels. I need space to fit better brakes, get suitable speed rated tyres and stop the backs spinning so easily.
Although the planed change from the standard 215 to 235/40R17 front and 235 to 255/40R17 rears is +20 both front and rear, the ratio is slightly altered. This choice is limited by available tyres sizes.
Am I likely to make one end more likely to let go because of the relative size change? Or is it likely to alter the slip angles and therefore make the car handle differently in terms of under/oversteer?
The usual choice with standard wheels is Toyo because there are few 15” choices. This is what I have and I like them, except for the above issues. But now I have more choice of tyres with 17”, what tyre do people think is better suited to the Griff?
The effect of going too wide seems to be that it could cause the tyre to suddenly let go when weight is transferred away from the tyre.
Has anyone fitted wider tyres and noticed an increased tendency to suddenly let go? If so, what sizes were fitted?
I have found quite a bit about increased grip with lower, wider tyres, but less about the traction. I have found that the standard rears are rapidly wearing and prone to wheelspin since the engine gained horses.
The car is nicely balanced at the moment on standard wheels, but I am changing to 17” wheels. I need space to fit better brakes, get suitable speed rated tyres and stop the backs spinning so easily.
Although the planed change from the standard 215 to 235/40R17 front and 235 to 255/40R17 rears is +20 both front and rear, the ratio is slightly altered. This choice is limited by available tyres sizes.
Am I likely to make one end more likely to let go because of the relative size change? Or is it likely to alter the slip angles and therefore make the car handle differently in terms of under/oversteer?
The usual choice with standard wheels is Toyo because there are few 15” choices. This is what I have and I like them, except for the above issues. But now I have more choice of tyres with 17”, what tyre do people think is better suited to the Griff?
hi Craig, from what I can remember its not so much the extra width on the tyre that makes it suddenly let go on cornering, but its the lower profile as the smaller sidewalls of the tyre do not flex as much as the higher sidewalls on the standard size tyre.
but then again I`m no expert on tyres I`m afraid.
but then again I`m no expert on tyres I`m afraid.
clive f said:
hi Craig, from what I can remember its not so much the extra width on the tyre that makes it suddenly let go on cornering, but its the lower profile as the smaller sidewalls of the tyre do not flex as much as the higher sidewalls on the standard size tyre.
but then again I`m no expert on tyres I`m afraid.
Sounds plausible. In that case if you fit Toyo T1R's on bigger rims, like i have, then the jelly sidewall may actually be about right. If a stiff sidewall is fitted with low profile then there may be even less flex. But how is this different to any other performance car? I appreciate the standard suspension is setup for the huge profile originals. but then again I`m no expert on tyres I`m afraid.
I was looking at this.
http://www.carbibles.com/tyre_bible_pg2.html
Plus things in other threads.
The comments were that wider tyres aren't always better.
I'm trying to find the optimum.
http://www.carbibles.com/tyre_bible_pg2.html
Plus things in other threads.
The comments were that wider tyres aren't always better.
I'm trying to find the optimum.
I did think hard about the 888’s and was very tempted.
Eventually I concluded that they’re not the right buy at the moment. I only take the car out if the weather looks right, except for long trips. If it weren’t for the long trips I would go straight to the 888’s, but I could get caught out on the long trips. Some of the local TVR crowd have 888’s. When the weather turns bad they have to slow right down and look all stressed.
We could easily find ourselves having to make a ferry back from France and pushing a bit too hard to catch it. Our RO recently lost his in France and he wasn’t even pushing or on 888’s. It brings it home. One son has just moved out to France, so now it’s not just occasionally visiting the holiday home, it’s frequent and not always at times of my choosing.
I think that ultimately what is needed is two sets of wheels, one with 888’s for the local good weather days and another set for going away for a while when we can’t be sure what the weather for the next week will be. I think getting the touring tyres right should come first, and then get some big brakes under them. When that’s sorted then I will look at the 888 set.
I spent this afternoon at the local Team Dynamics dealer measuring and looking at options. I see what you mean when you say that it’s close on the battery box Dave. That looks way too close for comfort with the 235/40 front. 215/40 on a 7.5 rim looks as much more sensible. I know it’s not recommended, but the 235/40 could probably be shoehorned onto the 7.5’s.
If I could be certain of the 8 X 17 ET25 fitting the front, then I would. That way I could be in a position to fit the 235/40 properly if it turns out there is enough room. I can’t see there being the room though. If there isn’t then I would have extra unsprung weight of the wider wheel for no reason.
The rears we are happy to go 9 X 17 ET40 and start with 255/40 R17. If they look to have enough clearance then I will try 265/40 when the 255/40’s need replacing.
Will the 8 X 17 ET25 and 9 X 17 ET40 definitely fit?
The makers say these are wider than they guarantee to fit, so if I order them and they don’t suit then I can’t send them back.
Eventually I concluded that they’re not the right buy at the moment. I only take the car out if the weather looks right, except for long trips. If it weren’t for the long trips I would go straight to the 888’s, but I could get caught out on the long trips. Some of the local TVR crowd have 888’s. When the weather turns bad they have to slow right down and look all stressed.
We could easily find ourselves having to make a ferry back from France and pushing a bit too hard to catch it. Our RO recently lost his in France and he wasn’t even pushing or on 888’s. It brings it home. One son has just moved out to France, so now it’s not just occasionally visiting the holiday home, it’s frequent and not always at times of my choosing.
I think that ultimately what is needed is two sets of wheels, one with 888’s for the local good weather days and another set for going away for a while when we can’t be sure what the weather for the next week will be. I think getting the touring tyres right should come first, and then get some big brakes under them. When that’s sorted then I will look at the 888 set.
I spent this afternoon at the local Team Dynamics dealer measuring and looking at options. I see what you mean when you say that it’s close on the battery box Dave. That looks way too close for comfort with the 235/40 front. 215/40 on a 7.5 rim looks as much more sensible. I know it’s not recommended, but the 235/40 could probably be shoehorned onto the 7.5’s.
If I could be certain of the 8 X 17 ET25 fitting the front, then I would. That way I could be in a position to fit the 235/40 properly if it turns out there is enough room. I can’t see there being the room though. If there isn’t then I would have extra unsprung weight of the wider wheel for no reason.
The rears we are happy to go 9 X 17 ET40 and start with 255/40 R17. If they look to have enough clearance then I will try 265/40 when the 255/40’s need replacing.
Will the 8 X 17 ET25 and 9 X 17 ET40 definitely fit?
The makers say these are wider than they guarantee to fit, so if I order them and they don’t suit then I can’t send them back.
spend said:
IF you have a battery box up in the wing, just cut it out & convert to the later arrangement.
Tyre selesction is a black art in itself, in light cars bigger is not always best.
I don’t know what the difference was between later cars and mine.Tyre selesction is a black art in itself, in light cars bigger is not always best.
There is definitely a protrusion into the F/N/S wheelarch of the right shape, size and position to be the back of the battery box. It’s not separate, but a bulge glassed into the inside of the wing.
What’s involved in its removal?
Would it push the battery back and reduce passenger legroom?
I have now grasped the fact that there is a limit to improving handling and traction by increasing size, but not how to discover what the limit is (without creating a TVR shaped topiary).
I have 245 tyres squashed onto the standard back rims. The car had them when I bought it. I’m starting to wonder if the squash is part of the problem.
Since the car gained the extra power (330bhp) it has spun the backs far too easily, although that could be partly due to the tyres being worn and needing replacement. What do think the optimum wheel and tyre sizes are?
I have 17" front with 225/40/17 and 18" rear with 245/35/18 Toyo T1R's. Cant get the car to understeer, and find the rear has the right balance. I have the same suspension setup as you (except arb mod) but thoroughly setup by TopCats. Think though that 18" rear is too low profile. It crashes a little. Convinced the tyre flex is too extreme under cornering and acceleration leaving the rim vulnerable on uneven road surfaces.
Chimjunkie said:
I have 17" front with 225/40/17 and 18" rear with 245/35/18 Toyo T1R's. Cant get the car to understeer, and find the rear has the right balance. I have the same suspension setup as you (except arb mod) but thoroughly setup by TopCats. Think though that 18" rear is too low profile. It crashes a little. Convinced the tyre flex is too extreme under cornering and acceleration leaving the rim vulnerable on uneven road surfaces.
Jon.... is the 18" problem down to tyre flex down on the Toyo's you are running having soft side walls and could be resolved by a tyre with aharder side wall ??I guess the problem is finding tyres soft enough compound, yet stiff enough tyre wall to work with the car weight and having the money to explore the market on what actuallly works
Hoover. said:
Chimjunkie said:
I have 17" front with 225/40/17 and 18" rear with 245/35/18 Toyo T1R's. Cant get the car to understeer, and find the rear has the right balance. I have the same suspension setup as you (except arb mod) but thoroughly setup by TopCats. Think though that 18" rear is too low profile. It crashes a little. Convinced the tyre flex is too extreme under cornering and acceleration leaving the rim vulnerable on uneven road surfaces.
Jon.... is the 18" problem down to tyre flex down on the Toyo's you are running having soft side walls and could be resolved by a tyre with aharder side wall ??I guess the problem is finding tyres soft enough compound, yet stiff enough tyre wall to work with the car weight and having the money to explore the market on what actuallly works
Hoover. said:
Chimjunkie said:
I have 17" front with 225/40/17 and 18" rear with 245/35/18 Toyo T1R's. Cant get the car to understeer, and find the rear has the right balance. I have the same suspension setup as you (except arb mod) but thoroughly setup by TopCats. Think though that 18" rear is too low profile. It crashes a little. Convinced the tyre flex is too extreme under cornering and acceleration leaving the rim vulnerable on uneven road surfaces.
Jon.... is the 18" problem down to tyre flex down on the Toyo's you are running having soft side walls and could be resolved by a tyre with aharder side wall ??I guess the problem is finding tyres soft enough compound, yet stiff enough tyre wall to work with the car weight and having the money to explore the market on what actuallly works
Chimjunkie said:
I have 17" front with 225/40/17 and 18" rear with 245/35/18 Toyo T1R's. Cant get the car to understeer, and find the rear has the right balance. I have the same suspension setup as you (except arb mod) but thoroughly setup by TopCats. Think though that 18" rear is too low profile. It crashes a little. Convinced the tyre flex is too extreme under cornering and acceleration leaving the rim vulnerable on uneven road surfaces.
I have also been advised to go 17” all round by the guy who will be setting up the suspension and I can live with the slightly different looks.I wanted to go for either the Toyo TR1’s, or the Goodyear Eagle F1 asymmetric that the same guy recommended.
The 225/40R17 would be about right, but neither the TR1, nor F1 is currently available in a 225/40R17, just a 225/45R17. That’s a difference that would put it outside the normal range of difference. The advice is to go for a wheel and tyre less than 2% different in diameter. The 225/4517 is 6.43% bigger and would add 38.3mm to the diameter.
Uncle Fester said:
The 225/4517 is 6.43% bigger and would add 38.3mm to the diameter.
Sure thats not the circumference? 5% of 225 is @ 10mm more 'protrusion' scraping the wheelarch IIRC. I think your selection should pay more attention to the design load of tyres available, the hardest criteria to fulfill is getting wide tyres not designed for bloated cars.IF your battery is up in the air (& fusebox on floor) its early with BIG step in the wheelarch, later battery is a box on the floor (if your car is on the cutover you may have a 'b
d') I don't think there is much difference in leg room due to the fitting angle of the foot plate? spend said:
Uncle Fester said:
The 225/4517 is 6.43% bigger and would add 38.3mm to the diameter.
Sure thats not the circumference? 5% of 225 is @ 10mm more 'protrusion' scraping the wheelarch IIRC. I think your selection should pay more attention to the design load of tyres available, the hardest criteria to fulfill is getting wide tyres not designed for bloated cars.IF your battery is up in the air (& fusebox on floor) its early with BIG step in the wheelarch, later battery is a box on the floor (if your car is on the cutover you may have a 'b
d') I don't think there is much difference in leg room due to the fitting angle of the foot plate? My car has the 205/50 R 15 tyres that were on it when I bought it, which aren’t right.
So referring to the bible for the correct fitment for my car, a 1994 500 with PAS. Steve said 215/50 R15.
So I plugged those numbers into an online tyre calculator with a comparison feature. On the other side I entered the 215/45 R17.
The results were 596mm diameter for the R15 and 634.3mm diameter for the R17 with a difference of 38.3mm. The circumferences were 1872.39, 1992.71 respectively with 120.32 difference.
The battery box I suspect to be the in between version. When I look in the wheel arch the battery box protrusion is not part of the wheel arch moulding.
It looks like someone knocked up a wooden former and laid glassfibre mat over it. This was then glassed over a hole to the battery area. There is no gel coat and it’s rougher than the surrounding glassfibre. My battery is low and the fuse box is above it.
I presume that the original body mould incorporated a big bulge. This was cut off and a bit glassed over like mine on the intermediate cars. Finally, a new mould to make the wheelarch with a proper battery box would be produced for the later cars. Is my assumption right?
I think you are probably right about the load rating of the tyres, but don’t understand enough on the subject. I have always thought of it as just ‘sidewall stiffness’ and those softer sidewalls suited lighter cars.
Am I right in thinking that what I am looking for is a load rating that is high enough to withstand the load, but not massively over it, because that would have stiffer sidewalls.
Looking at Toyo TR1 range, the R15 tyres have a load index of between 78 (425kg) and 89 (580kg).
The R16 TR1’s range between 80(450kg) and 100 (800kg).
The proposed TR1 fitments of 215/40R17 is 87 (545kg) and 245/40 R17 is 94(690kg) the actual sizes that should be fitted to my car are only 15-20kg off. So the stiffness should change very little.
If I am getting this right then the tyre ratings should be the weight of the car divided by four plus a 20% safety margin on a car with a 50/50 front/rear weight balance. If the car isn’t 50/50 then this would have to be allowed for.
The car weighs 1060kg, so that suggests the right loading should be about 318kg, or a load index of about 68-69.
I still haven’t figured out what the W or Y after the load index means.
Do I understand this lot right Dave?
I notice that some of the TR1’s are marked ‘RF’. Are these ones run-flat?
Edited to add.
I just realised that I based the above on unlaiden weight of the car. I will have to alter the load index accordingly.
Edited by Uncle Fester on Wednesday 22 October 08:14
Something you might not have considered is weight.
I spend a morning swapping wheels over on my T350 to SEAC and also weighed the wheels.
The 18 inch spiders weights 2 kg more each !
Seac wheels were about 15kg, spiders 17kg.
This was something that Peter Wheeler resisted around the time of the chim / griff - as he did not want big wheels spoiling the handling of his cars.
Guess time and fashion eventually forced the change to bigger wheels.
Handling - well OK they are totally different cars but the handling on the limit for each is very much down to the tyres - the SEAC will drift and slide (225/50 15) and T350 would eventually just snap and left go .. and spin (245/40 18).
Just to let you know there is a down side to the big wheel look. Sorry.
I spend a morning swapping wheels over on my T350 to SEAC and also weighed the wheels.
The 18 inch spiders weights 2 kg more each !
Seac wheels were about 15kg, spiders 17kg.
This was something that Peter Wheeler resisted around the time of the chim / griff - as he did not want big wheels spoiling the handling of his cars.
Guess time and fashion eventually forced the change to bigger wheels.
Handling - well OK they are totally different cars but the handling on the limit for each is very much down to the tyres - the SEAC will drift and slide (225/50 15) and T350 would eventually just snap and left go .. and spin (245/40 18).
Just to let you know there is a down side to the big wheel look. Sorry.
Edited by rev-erend on Wednesday 22 October 09:18
The point about weight is that if you buy tyres capable of carry 10 times as much weight as your car, the load is just not enough to get them in the op range of the compounds. Use it as an additional guideline to get suitable tyres. There was a lot of PH crap dumped on Toyos when some people were referring to the TVR specific versions and others to the Generic T1-S, they had different load ratings, & hence completely different characteristics. Most cars in the same class as TVR, unfortunately are much heavier and hence suitable tyres are primarily designed for different criteria. Also as in the TVR case history, tyres that are suitable one year may be discontinued due to lack of demand.
Instead of pharting about with pipe & ecu group buys, the TVR community should attempt to get a deal with a tyre manufacturer to produce suitable tyres IMHO.
The W & Y are the speed ratings.
As Alan said weight of wheels is very important, most people choose wheels for aesthetics however.. IIRC the SP wheels have an advantage in this dept.
Instead of pharting about with pipe & ecu group buys, the TVR community should attempt to get a deal with a tyre manufacturer to produce suitable tyres IMHO.
The W & Y are the speed ratings.
As Alan said weight of wheels is very important, most people choose wheels for aesthetics however.. IIRC the SP wheels have an advantage in this dept.
rev-erend said:
Chimjunkie said:
Rev, what are the tyre make and models? Will have to measure the weight of my 17/18" compared with the 15/16" out of interest now.
Pretty sure they are all TOYO.I've used 888's on the SEAC - too scary in the wet - so won't buy them again.
TR1s and TR1R ..
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