Technically I'm tyred!
Discussion
Apologies if this has been asked before 'cause I suspect that this may be an old query, but since I'm pretty new here....
1) I'm due a tyre change - currently running S02s 255/35zr18 rr and 225/35zr18 fr
2) Can't get a full set of S02s, so looking at Proxes
3) Recommended Proxes are a higher profile tyre:
- rears are 245/40 ie 40% of 245mm = rather than 35% of 255mm for the Bridgestones)
- fronts are 235/40 instead of 225/35
which presumably means that the total wheel radius (hub radius plus tyre wall depth) is greater.
4) QED, the Proxes have a larger circumference - if my dodgy fag packet calculations are corrrect a little short of 3% bigger circumference for the fronts and about 1.6% at the rear.
Question 1 - does this mean that the Speedo needs to be recalibrated, since 1 wheel revolution will now take me further and if achieved in the same time will mean that I am moving faster than indicated ?
Question 2 - Is there any problem with fitting or running the different width Proxes to the current rims ?
Question 3 - Does the different sized tyre affect suspension/damper etc settings in any way that I should know about ?
Question 4 - what are the recommended tyre pressures for the Proxes
Further apologies where necessary for:
1) poor recollection of my 'O' level maths
2) poor understanding of the workings of a speedo
3) any other general 'dufferliness'
Cheers
Lax
1) I'm due a tyre change - currently running S02s 255/35zr18 rr and 225/35zr18 fr
2) Can't get a full set of S02s, so looking at Proxes
3) Recommended Proxes are a higher profile tyre:
- rears are 245/40 ie 40% of 245mm = rather than 35% of 255mm for the Bridgestones)
- fronts are 235/40 instead of 225/35
which presumably means that the total wheel radius (hub radius plus tyre wall depth) is greater.
4) QED, the Proxes have a larger circumference - if my dodgy fag packet calculations are corrrect a little short of 3% bigger circumference for the fronts and about 1.6% at the rear.
Question 1 - does this mean that the Speedo needs to be recalibrated, since 1 wheel revolution will now take me further and if achieved in the same time will mean that I am moving faster than indicated ?
Question 2 - Is there any problem with fitting or running the different width Proxes to the current rims ?
Question 3 - Does the different sized tyre affect suspension/damper etc settings in any way that I should know about ?
Question 4 - what are the recommended tyre pressures for the Proxes
Further apologies where necessary for:
1) poor recollection of my 'O' level maths
2) poor understanding of the workings of a speedo
3) any other general 'dufferliness'
Cheers
Lax
Take a look at www.pistonheads.com/gassing/topic.asp?t=23475&f=13&h=0&hw=S02
It's actually a more balanced review than I remembered.
It's actually a more balanced review than I remembered.
Lax, I am afraid your maths is slightly out. The suggested change is not good at all:
Front - Original rolling circumference 1931mm
suggested new rolling circumference 2027mm an increase of 4.7%, far too high to consider.
Rear - Original rolling circumference 1997mm
suggested new rolling circumference 2052mm an increase of 2.7%, also too high.
I consider a maximum change of 1.5-1.7% to be reasonable.
Answer to question 1 = probably as 2.7% is quite a lot and yes you would be going 2.7% faster than before
Answer to question 2 = tyres would probably fit OK but I would not do it.
Answer to question 3 = Yes. The change you are suggesting will also alter the balance of the car, narrower rear and wider front will promote oversteer. Also the increase in radius will lift the front of the car by 17.5 mm and the rear by 8.75 mm (exactly half), thus changing the airflow reducing stability, the front will probably lift at speed.
Answer to question 4 = The same as before will give you the same tyre contact patch size, although it will be a slightly different shape. You are not altering the weight of the car itself.
Sorry to put a damper on the idea but I think your tyre dealer is trying to sell you anything he has rather than getting what you need.
Front - Original rolling circumference 1931mm
suggested new rolling circumference 2027mm an increase of 4.7%, far too high to consider.
Rear - Original rolling circumference 1997mm
suggested new rolling circumference 2052mm an increase of 2.7%, also too high.
I consider a maximum change of 1.5-1.7% to be reasonable.
Answer to question 1 = probably as 2.7% is quite a lot and yes you would be going 2.7% faster than before
Answer to question 2 = tyres would probably fit OK but I would not do it.
Answer to question 3 = Yes. The change you are suggesting will also alter the balance of the car, narrower rear and wider front will promote oversteer. Also the increase in radius will lift the front of the car by 17.5 mm and the rear by 8.75 mm (exactly half), thus changing the airflow reducing stability, the front will probably lift at speed.
Answer to question 4 = The same as before will give you the same tyre contact patch size, although it will be a slightly different shape. You are not altering the weight of the car itself.
Sorry to put a damper on the idea but I think your tyre dealer is trying to sell you anything he has rather than getting what you need.
andyvdg said: Shouldn't you get the same size tyres, but with the higher profile ? e.g. 255/40 ? Or am I missing something ?
The idea in general terms is to replace the tyres like for like, or, if changing rim size, to keep the rolling radius approximately the same. If changing the profile of the tyre only you are also altering the car's ride height, gearing and handling.
Yeah, but you are keeping the ride height relative from front to back the same. Otherwise don't you change the width of both the front and back tyres as well as the profile, and as discussed don't get quite the same front/back height ratio ? Which is more important ?
Don't know - I'm on S02 / 40s at the moment, so I'm hoping if I go for Toyos I can get the same size. I've seen S03s on a Tuscan and I don't like them just because there is no rim protector as you get on the S02s.
Cheers,
Andy.
Don't know - I'm on S02 / 40s at the moment, so I'm hoping if I go for Toyos I can get the same size. I've seen S03s on a Tuscan and I don't like them just because there is no rim protector as you get on the S02s.
Cheers,
Andy.
Changing the ride height (increasing it) raises the Center of Gravity as well as allowing more air to flow under the car, both of these may have negative handling aspects.
The gearing will also be changed but may not make much difference because the change may be insignificant. In general to increase the rolling circumference slows a car down (in acceleration) because each gear will take you to a higher speed than before. Top speed may also be reduced if power at the lower engine speed cannot overcome the drag.
If you maintain the width but increase the profile you are actually increasing drag because you have increased the frontal area (if you do not lower the suspension to compensate).
Normally performance car manufacturers put the optimum tyre size on the car (but for TVR may depend on what was available?
). I do not personally recommend changing tyre sizes for normal road use.
All my comments are made in good faith, but I am not a motor engineer, just an enthusiast so I may make mistakes!
The gearing will also be changed but may not make much difference because the change may be insignificant. In general to increase the rolling circumference slows a car down (in acceleration) because each gear will take you to a higher speed than before. Top speed may also be reduced if power at the lower engine speed cannot overcome the drag.
If you maintain the width but increase the profile you are actually increasing drag because you have increased the frontal area (if you do not lower the suspension to compensate).
Normally performance car manufacturers put the optimum tyre size on the car (but for TVR may depend on what was available?
). I do not personally recommend changing tyre sizes for normal road use. All my comments are made in good faith, but I am not a motor engineer, just an enthusiast so I may make mistakes!
I thought Toyos are the make of 18" tyres supplied on new Tuscans. A quick look on the website confuses the issue again as they quote sizes 225/35 and 255/35 i.e. back to 35 profile again.
So if you're on 35s should you stay on 35s ? Should I replace mine with same 40s but a different make or go onto 35s ? I don't know the size of my 40s - I'll have to check before I drive off home.
So if you're on 35s should you stay on 35s ? Should I replace mine with same 40s but a different make or go onto 35s ? I don't know the size of my 40s - I'll have to check before I drive off home.
Ditto the above really. My Tuscan was running low profile Bridgestones when it was new. It now has a Toyo Proxes T1-S all round - rears are 245/40 ZR 18, fronts are 235/40 ZR 18. The slightly higher profile means (day to day) - much reduced tramlining, more comfortable and better placed ride quality, and of course less kerbing with pot holes.
My car's tyres were changed at Michaeldever and treated to a 4 wheel re-alignment to later settings which makes the car steer and handle much better than when original. If anyone wants the suspension settings email me off line and I'll put them into a spreadsheet.
But to answer your question, the new Toyos suggested to you are fine and what the factory fitted to all new Tuscans from around mid 2001 onwards.
My car's tyres were changed at Michaeldever and treated to a 4 wheel re-alignment to later settings which makes the car steer and handle much better than when original. If anyone wants the suspension settings email me off line and I'll put them into a spreadsheet.
But to answer your question, the new Toyos suggested to you are fine and what the factory fitted to all new Tuscans from around mid 2001 onwards.
Nick Elliott said: I upgraded from 16" to 18" wheels and Toyo tyres,the fronts are 235/40/18 and rears 245/40/18.The speedo reads the same for a given engine RPM so the rolling radius must be about the same.
Nick
Not necessarily so because the speedo drive is taken from the gearbox, therefore it will always be the same for any given engine speed, it just may not be the same roadspeed.
If you post the original tyre sizes I can let you know the differences, if any.
TVR did modify the suspension pick up points around autumn 2001 and I think that was around the time Toyos were introduced as standard - so I would say yes.
I drove a demo car earlier that year when I was thinking of changing from the Chim - so it would have been on the old suspension with the low profile Bridgestones. It was terrible! The tramlining was so pronounced that I left the showroom feeling disappointed in the Tuscan. However, having driven some other cars I invested in my mine, a late 2000 model. This had the Bridgestones as OEM but when they worn out they were replaced with the Toyos and the suspension geometry set to the Tuscan RR settings as published on the ToG. Unbelievable! And having driven later cars than mine, T cannot tell the difference.
Although I have no personal experience of this, I gather from older threads that TVR have a reputation for being a little slap dash with suspension settings on new cars leaving the factory. I would certainly recommend taking a car to someone who knows what they are doing and getting a 4 wheel alignment. Not expensive and can make a dramatic improvement on some cars.
I drove a demo car earlier that year when I was thinking of changing from the Chim - so it would have been on the old suspension with the low profile Bridgestones. It was terrible! The tramlining was so pronounced that I left the showroom feeling disappointed in the Tuscan. However, having driven some other cars I invested in my mine, a late 2000 model. This had the Bridgestones as OEM but when they worn out they were replaced with the Toyos and the suspension geometry set to the Tuscan RR settings as published on the ToG. Unbelievable! And having driven later cars than mine, T cannot tell the difference.
Although I have no personal experience of this, I gather from older threads that TVR have a reputation for being a little slap dash with suspension settings on new cars leaving the factory. I would certainly recommend taking a car to someone who knows what they are doing and getting a 4 wheel alignment. Not expensive and can make a dramatic improvement on some cars.
kevinday said:
Nick Elliott said: I upgraded from 16" to 18" wheels and Toyo tyres,the fronts are 235/40/18 and rears 245/40/18.The speedo reads the same for a given engine RPM so the rolling radius must be about the same.
Nick
Not necessarily so because the speedo drive is taken from the gearbox, therefore it will always be the same for any given engine speed, it just may not be the same roadspeed.
If you post the original tyre sizes I can let you know the differences, if any.
The original fronts were Bridgestone SO2’s front 205/50/16 rear 225/50/16 the diameter of the original rears is 24.8 inches the new rear tyre diameter is 25.7 inches. The difference in revs per mile is 836 (16”) 807 (18”) is 29 revs per mile so the difference in circumference is 77.911 (16”) 80.7389 (18”) = 2.8279 inches so that’s about 82 inches per mile ie not really noticeable on the speedo.
Nick
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