Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Tyre size 2015 (!) Roadster3.7

Is there anybody with a recent Roadster 3.7 and the 6,5x15" black wire wheels around?

There are some ambiguities about the correct size either on the car and in MMC´s "CoC" (Certificate of Conformity).

My current Roadster is irritatingly fitted with the lower profile 205/60-15 versus (correct, at least up to now) the higher profile 205/65-15 (resulting in a quite painful poor ground clearance).

So any qualified answers would be very welcomed!

The 65s have a diameter of 25.5 when new, the 60s 24.7, so a gain in 0.8 of an inches or in terms of ride height only 0.4 of and inch or about 10mm.

I currently have AVON CR5 205/65 15's and have a nice ride height. If you pop out to the garage and measure from th ground the to chassis rail at the back axle each side and the centre point of the tube on the header frame to the ground, I can do the same and we can compare ride heights.

I was actually thinking of going to 60's next time, but we'll see.

I recently changed from 60 to 65 profile for my Plus 4, I would not revert back.
That extra 10 mm does make a difference when going over road humps etc.

I have the Avon 205/65 R 15 original fitted and have no problems with ground clearance.

Jochen. I have sent you an email. Let me know if you don't receive it.

Attached to this post is a pdf file giving tyre size comparisons.

Note that it refers to the proposed fitting of a 195/65 R15 to a Plus 4 but it also includes the tyre sizes Jochen is referring to. Note also that the fitting of a 205/65 R15 would allow you to use a 4/4 wheel with a 165/80 R15 tyre as a "space saver" spare. If you have a spare you need to check that the tyre will fit the space as the diameter is increased by aprox. 2 cm.

If you are going to compare ride heights as a result of tyre profiles, that's not the right way to check as it will be affected by spring sag etc! You need to measure from the axle to the ground.

Err! Jays, the table gives tyre radius (amongst other things) which, whatever the state of the springs, a change in tyre size has a bearing on the ground clearance. The radius equals the approximate (the variable being tyre pressure) distance of the centre of the axle from the ground.

If you want a quick method of comparing the springs component of ride height for different cars I can give you that too.

Changing from a 205/60 tyre to a 205/65 profile will increase the radius, and therefore the ride height, by about 10mm. The slash profile number represents a percentage of the tyre width. In this case, 205 is the width and the profile height is 65% of the width.

Would /65 fit in the spare hole?
Have you tested it?
It does sound a bit marginal although the curved sidewall will help. Because an odd sized spare & LSD are not good bedfellows.

It just fits with 5mm clearance. The main difficulty is the snorkle brake light which takes up about 8mm at the top so you finish up with a slight offset towards the bottom. Better to order to the 65 profile tyres when you order the car, then you get the right sized hole.

Not interested in axle to ground but actual ground clearance Jays, as this is Jochens issue. I was trying to compare mine with his and then we can work out where the difference is apart from the tyre difference.