bi22le
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| posted on 17/6/10 at 09:41 AM |
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wheel offset from et38 to et35. Is this ok?
following on from my previous post im thinking of getting a set of 15"wheels for track use so i can use slicks for cheap.
Problem is my striker runs on et38 offset and standard cossies use et35 which are the wheels im looking at. Is this a big difference? Im going to
check the clearance between my caliper and wheel. What else should i check?
Is it even a wise move changing to 15" from 14" just to get cheap slicks?
Thanks for your help, as always.
Biz
Track days ARE the best thing since sliced bread, until I get a supercharger that is!
Please read my ring story:
http://www.locostbuilders.co.uk/forum/13/viewthread.php?tid=139152&page=1
Me doing a sub 56sec lap around Brands Indy. I need a geo set up! http://www.youtube.com/watch?v=EHksfvIGB3I
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loggyboy
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| posted on 17/6/10 at 10:18 AM |
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Does the width change?
if not then this only means that you end up with the wheel sitting 3mm further out, which unless your arches are tight up against the wheel then it
shouldnt be a problem
If the width changes aswell then you need to add half of the width increase to each side of the wheel, in addtion to the 3mm.
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nick205
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| posted on 17/6/10 at 10:28 AM |
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Wouldn't it be cheaper all round (and better) to go to 13" rims and slicks?
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Humbug
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| posted on 17/6/10 at 10:40 AM |
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Assuming that the wheel is the same width overall, then the change is just 3mm. I would just checked current clearance then work out if 3mm extra in
whichever direction would be likely to foul anything (I think that going from 38 to 35 would make the wheel rim move 3mm further out from the
hub)
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jeffw
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| posted on 17/6/10 at 10:47 AM |
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13" wheels will make the car handle better than 15" ones.
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loggyboy
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| posted on 17/6/10 at 11:15 AM |
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quote:
Originally posted by jeffw
13" wheels will make the car handle better than 15" ones.
Cant see your logic there, lower profile tyres aid handling, 195 50 15s would better than the equivelent circumference 13" tyres.
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Chet
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| posted on 17/6/10 at 11:16 AM |
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FYI -
I've found this tool to be very useful.
http://marksink.com/tire_wheel_offset/offset.html
You should also consider the weight of the various solutions.
Chet
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andkilde
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| posted on 17/6/10 at 11:37 AM |
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quote:
Originally posted by loggyboy
quote:
Cant see your logic there, lower profile tyres aid handling, 195 50 15s would better than the equivelent circumference 13" tyres.
Not quite as simple as that, lower profile can equal less sidewall flex, which is sometimes an advantage (relatively heavy saloons with hard springs
and lots of tyre pressure comes to mind as one example). Sevens are light and run fairly low tyre pressures in order to get enough heat into the
tyres, a bit of extra sidewall flex can aid in keeping the tyre in contact with the road and be advantageous, not to mention the benefits of lower
unsprung weight, which is a bigger deal on a light car, proportionally.
Cheers, Ted
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loggyboy
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| posted on 17/6/10 at 12:13 PM |
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quote:
Originally posted by andkilde
Not quite as simple as that, lower profile can equal less sidewall flex, which is sometimes an advantage (relatively heavy saloons with hard springs
and lots of tyre pressure comes to mind as one example). Sevens are light and run fairly low tyre pressures in order to get enough heat into the
tyres, a bit of extra sidewall flex can aid in keeping the tyre in contact with the road and be advantageous, not to mention the benefits of lower
unsprung weight, which is a bigger deal on a light car, proportionally.
Cheers, Ted
I can understand the tyre argument, but I would expect the difference in weight would be minimal (if any) as the amount of metal in the hub is the
same, the circumference only slighly less and spoke size would also be only a tiny increase. Further to that you would also have an increase in tyre
weight due to the larger profile.
I often assumed F1 cars had smaller wheels because of these reasons, but i recently heard it mentioned on the BBC coverage that the teams would like
to use larger wheels and smaller profile tyres as its only the regs that keep them using small wheels.
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bi22le
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| posted on 17/6/10 at 12:20 PM |
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Hmm weight is a good point and I understand that 13" would be the ideal but to fit them on a Striker I need different wish bones, caliper mods
and a geometry set up. Thats more than just slapping a set of 15" on!
The wheels are getting wider so I think Ill have to check for clearences tonight. It would look nice on 15" cossie cross weave wheels. With
slicks on aswell the grip should be better that 13" with semi cuts I would of thought.
Oh, I didnt mean to spark off the 13" thick wall vs 15" thin wall argument by the way.
RE did anybody else read the post copied from the VXR forum following a chat with Mr Toyo. He was saying that the tyres work best at mid to high
twenties not eighteen PSI.
Thanks for the responses
Track days ARE the best thing since sliced bread, until I get a supercharger that is!
Please read my ring story:
http://www.locostbuilders.co.uk/forum/13/viewthread.php?tid=139152&page=1
Me doing a sub 56sec lap around Brands Indy. I need a geo set up! http://www.youtube.com/watch?v=EHksfvIGB3I
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flak monkey
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| posted on 17/6/10 at 02:48 PM |
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Having just changed from 15" rims to 13" rims I can vouch for the big differences they make.
The ride is much better, less harsh over the bumps, but I havent noticed any difference in the handling and responsiveness.
As far as the OP post goes - 3mm difference doesnt matter on the offset, they will stick out another 3mm assuming the same rim width.
Weight wise, theres about 2kg per corner advantage, even with the massive 8" rims i put on the back. The tyres weigh about the same, but the
rims are a lot lighter.
Sera
http://www.motosera.com
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iank
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| posted on 17/6/10 at 04:52 PM |
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quote:
Originally posted by loggyboy
I can understand the tyre argument, but I would expect the difference in weight would be minimal (if any) as the amount of metal in the hub is the
same, the circumference only slighly less and spoke size would also be only a tiny increase. Further to that you would also have an increase in tyre
weight due to the larger profile.
The weight difference is actually quite a lot. Circumference of a 13" wheel is 1037mmm
Circumference of a 15" wheel is 1197mm so about 15.5% more weight, say 16% overall to account for additional spoke thickness for an otherwise
identical design.
However the effect of the weight is more than that since it's an inch further from the hub so all the rotational issues get that much worse.
Low profile tyres also weigh the same or slightly more than an equivalent circumference 13" in my experience due to the thicker tyre walls they
use, though I have no idea whether slicks are the same in that department.
Finally I'd be cautious of comparing F1 tyres with 'real' cars. Since the 80's they've effectively been using the tyre
as the only sprung suspension component (take a look at the movement - or lack of it - on the front wishbones from the on-board cameras) If they
fancy a change of tyre aspect ratio they have their reasons but they're may have more to do with brake cooling and tyre temperature control than
suspension design and handling.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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