Discussion
All
Im looking at upgrading my wheels to 18" rear and 17" front. Can anyone let me know of anything that I need to consider eg
- Any problems with 'over filling' the wheel arch ie rubbing?
- Any adjustments needed to suspension as the wheel arches are fuller?
- Any issues with odometer,speedometer readings due to the larger circumeference?
Im guessing that a number of these concerns may be overcome due to having lower profile tyres. With the lower profile tyres what is the ride like? Also does it affect handling?
Excuse my ignorance on this but those who know me well enough will know i dont know much
Cheers
Im looking at upgrading my wheels to 18" rear and 17" front. Can anyone let me know of anything that I need to consider eg
- Any problems with 'over filling' the wheel arch ie rubbing?
- Any adjustments needed to suspension as the wheel arches are fuller?
- Any issues with odometer,speedometer readings due to the larger circumeference?
Im guessing that a number of these concerns may be overcome due to having lower profile tyres. With the lower profile tyres what is the ride like? Also does it affect handling?
Excuse my ignorance on this but those who know me well enough will know i dont know much
Cheers
Fit lower profile tyres so the total circumferance is the same? You can usually get it within a couple of percent so you won't notice any speedo error. Chances are you have 10%+ error anyway if mine's anything to go by.
You may get rubbing problems if you go much for much wider tyres, but I doubt you will so it shouldn't be a problem.
As for handling - there will definitely be a change. You effectively stiffen up your suspension by vastly reducing the spring effect of the tyre sidewalls. I had to put the softer set of springs on my Scoob when the 18" rims went on to get the ride quality back. This created increased "normal" suspension travel, but since the dampers & springs were much more predictable than the combined effects of springs, dampers and the old tyres the car was much more composed on the road. The extra body roll was dealt with by having slighly larger ARBs.
I've driven one Griff with 18" spiders on (Thanks Bananaman
) and it handled just fine while "making progress" on reasonable A & B roads.
What do I know though? I'm sure you'll wake the suspension experts up soon enough
You may get rubbing problems if you go much for much wider tyres, but I doubt you will so it shouldn't be a problem.
As for handling - there will definitely be a change. You effectively stiffen up your suspension by vastly reducing the spring effect of the tyre sidewalls. I had to put the softer set of springs on my Scoob when the 18" rims went on to get the ride quality back. This created increased "normal" suspension travel, but since the dampers & springs were much more predictable than the combined effects of springs, dampers and the old tyres the car was much more composed on the road. The extra body roll was dealt with by having slighly larger ARBs.
I've driven one Griff with 18" spiders on (Thanks Bananaman
) and it handled just fine while "making progress" on reasonable A & B roads. What do I know though? I'm sure you'll wake the suspension experts up soon enough
I agree with Dave, but I would just upgrade the bushes & drop links on the ARBs which should be enough.
Spiders are wider wheels & you just lose a bit of lock on the front (stops are only cheap plastic washers ~ take 5min to fit). Just make sure your offsets are right, as long as you are sensible on wheel width & tyre selection you should have no problems. I would'nt do it unless you have decent adjustable dampers and are prepared to play with them tho!
Dave
Forgot: It does sound like Silverstone do wheels specifically suited to our cars...
Spiders are wider wheels & you just lose a bit of lock on the front (stops are only cheap plastic washers ~ take 5min to fit). Just make sure your offsets are right, as long as you are sensible on wheel width & tyre selection you should have no problems. I would'nt do it unless you have decent adjustable dampers and are prepared to play with them tho!
Dave
Forgot: It does sound like Silverstone do wheels specifically suited to our cars...
Edited by spend on Thursday 15th March 13:12
I made this spreadsheet a while back - it shows how close you can get the tyre sizes for different rims:
Tyre Width Tyre Profile Rim Diameter % Difference
225 50 15 100.00%
225 45 16 100.48%
235 40 17 102.28%
245 45 16 100.00%
245 40 17 100.14%
245 35 18 100.29%
255 40 17 101.42%
Hopefully it's even correct too, even if it is badly formatted!
Tyre Width Tyre Profile Rim Diameter % Difference
225 50 15 100.00%
225 45 16 100.48%
235 40 17 102.28%
245 45 16 100.00%
245 40 17 100.14%
245 35 18 100.29%
255 40 17 101.42%
Hopefully it's even correct too, even if it is badly formatted!
Edited by dnb on Thursday 15th March 11:35
Graham,
I know that there are a couple of Griffs about with 18" rims but, much of our suspension comes from the compliance in the side wall of the tyre (one of the reason why our stock tyres have quite high aspect ratio for a sportscar), so it will make ride much harsher in my opinion.
I have gone for 17" all round and with a few tweaks to suspension geometry still give a reasonably compliant suspension. What is important is the width of the rims 7.5J on the front is fine but you do really need 8.5 - 9J on the rear in order to run a 245 tyre width. When I was looking for alloys it was the rear widths that seriously reduced my options.
I know that there are a couple of Griffs about with 18" rims but, much of our suspension comes from the compliance in the side wall of the tyre (one of the reason why our stock tyres have quite high aspect ratio for a sportscar), so it will make ride much harsher in my opinion.
I have gone for 17" all round and with a few tweaks to suspension geometry still give a reasonably compliant suspension. What is important is the width of the rims 7.5J on the front is fine but you do really need 8.5 - 9J on the rear in order to run a 245 tyre width. When I was looking for alloys it was the rear widths that seriously reduced my options.
That's interesting. I was just told that a 8" rear would be fine for a 245 tyre - aren't the TVR originals 7.5" wide as standard?
My 17"s will be in a 7" and 8" with original offsets using 215/40 and 245/40 Toyos and I'm hoping for an improvement in road manners over the current horrid S02/S03 mixture I'm enduring!
eta: With these tyre sizes I'm within a couple of percent original wheel sizes.
dumbfunk
My 17"s will be in a 7" and 8" with original offsets using 215/40 and 245/40 Toyos and I'm hoping for an improvement in road manners over the current horrid S02/S03 mixture I'm enduring!
eta: With these tyre sizes I'm within a couple of percent original wheel sizes.
dumbfunk
Edited by dumbfunk on Thursday 15th March 14:51
TVR fitted 245 rears on 7.5 rims and it is within the tyre fitting spec but not ideal. Most tyre fitting details show 8.5 as the ideal rim for 245 but these do seem to be a challenge to find in an offset and PCD to fit. A couple of people will make them but they are a tad expensive. I have just got 7.5x17 front and 8x17 rear pro race 1.2 rims. Sticking with 245 rears so not ideal but slightly better than the original. People have fitted 9 inch rears (and there are a few choices around) but it all starts to look a bit tight.
Rubber is being fitted to rims right now so fingers crossed all will be OK.
Rubber is being fitted to rims right now so fingers crossed all will be OK.
steve-v8s said:
I have just got 7.5x17 front and 8x17 rear pro race 1.2 rims.
Hi Steve
I've gone for the same wheels but in a 7" front intending to run a 215/40. I assume you're intending to up to a 225 for the 7.5" right?
[eta: just found this interesting application chart and either is good www.toyo.co.uk/productdetail.php?identity=products&product_id=2 ]
dumbfunk
Edited by dumbfunk on Thursday 15th March 16:50
steve-v8s said:
TVR fitted 245 rears on 7.5 rims and it is within the tyre fitting spec but not ideal.
True but remember that the car started with 225/50/16 on the rear which is a fairly nice fit on the 7.5" rims. TVR then changed the tyre but appeared to have a load of wheels... A 245 would generally be best on 8.5" rims.
FlipFlopGriff said:
jeffsy said:
Excuse my ignorance on this but those who know me well enough will know i dont know anything
Cheers
What you doing with the estorils?
FFG
ermmm...dont know yet mate...whether to keep them as spares (Kemble in June??) or sell. They are in v v good nick so would probably cover the cost (most of it anyway) of a new set.
In answer to some of the other points I have poly bushes all round, adjustable shocks and SH droplinks also so thats all covered. I would want to keep the larger at the back and smaller at the front combo...
What you also have to remember, is that on 16" rims and 50 aspect ratio the sidewall angle is not so accute. Increasing to 17"/18" the side wall gets much small to maintain the rolling diameter so the side wall angle becomes much more accute as it is drawn in for a 7.5J rim which increases the tendancy for "rim roll" in cornering.
This was my mistake and with going to softer Toyo Poxies it is noticable on my car, so when these tyres are shot i will be getting two new wider rear rims.
This was my mistake and with going to softer Toyo Poxies it is noticable on my car, so when these tyres are shot i will be getting two new wider rear rims.
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