Tyre sizes

Post by **Gayno** » Mon Apr 30, 2012 3:53 pm

I think you've got a bit mixed up here in how much your car will lower by running a lower profile tyre.

the 45/50/55 of the tyre size is not mm, it is the percentage of the tyre width. so a 205/50 tyre, the profile will be approx 100mm. Meaning the difference between 55 and 50 is only 10mm, and a further 10mm to a 45, all on a 205 width tyre.

Post by **Merlin** » Mon Apr 30, 2012 3:58 pm

^^Reps!

bristol_bb4 · Post by **bristol_bb4** » Mon Apr 30, 2012 3:59 pm

+ rep for that adam, i didnt know that

A1ex · Post by **A1ex** » Mon Apr 30, 2012 3:59 pm

I know about the profile %age, I'm changing the wheel diameter from 17" to 16" so keeing the same profile will drop the ride height by 1/2" on top of a 30mm with the teins.

Post by **Gayno** » Mon Apr 30, 2012 4:11 pm

Provided the tyre width is the same!

If it is the same, get the next size profile up and that will then negate the height drop due to the wheel change.

A1ex · Post by **A1ex** » Mon Apr 30, 2012 4:55 pm

Ok, I think were getting lost here.

I know how the tyre sizing works, that's not the question. what I want to know is if I drop the height of the car by 1/2" through changing the wheels from 17" to 16" and keeping the same tyre proportions of 205/45. Then lower it a further 30mm on the suspension, will the total lowering of 45mm ish be too much for driving over speed bumps and bad roads?

I'd like to reduce the overall wheel size to increase the acceleration a little, but if it's going to cause problems then I'll maintain the current wheel size and fit the teins

Post by **Gayno** » Mon Apr 30, 2012 5:03 pm

Ah OK! Your thread title being "tyre sizes" implies your question is just that!

My 4th is currently about 45mm lower, with a deep front lip on, I can get over the little speed humps, but have to go slow over normal ones. I did catch it on something yesterday though and cracked the lip

but it is a deep lip compared to OEM or most others.

Post by **Donald** » Mon Apr 30, 2012 5:07 pm

I think you should be fine, so long as you're mindful of any speed bumps and horrible country roads.

I'm lowered about 45mm just with suspensionings and on 17s. (went out a while ago but still forgot to see what tire sizes I was running) and the only issues I have are with those plasticky mud flaps and the cat. I'm quite attached to the flaps (;)) but so long as I don't go racing over bumps they don't catch, same for the cat. As for country roads... I get the odd flap scrape if I hack around a corner

Hope that sort of helps

A1ex · Post by **A1ex** » Mon Apr 30, 2012 5:09 pm

Ok good stuff, not the lip obviously that's bad stuff! So I can reduce the wheel size a little and drop the ride height without running into major problems. I need to two wheel over the pillow speed bumps now anyway rather than straddling them, I had a look at the very inside edge of the tyres and they're wearing through from all the speed humps round in my area!

My dad changed his last weekend and was on the brink of a blow out from the wear even though he had about 3mm tread left above all of the depth indicators

Post by **RattyMcClelland** » Mon Apr 30, 2012 7:08 pm

Imo you have 3 choices on 16".

205/50/16
215/45/16
225/45/16
225 would be the limit for 7" and all tyres vary in width even though they will state 225.
Iv seen Uniroyal rainsport 2 on a 17x7 Saab wheel and its looks spot on.

Today i pick up a set off 225/45/16 AD08s off ebay for a bargain.

They are going on my 16x7. AD08 run a bit wider bit will work fine. I wanted to keep as close to the stock side wall as possible and 205/50 and 225/45 are the same.