SHORT LEGS

Mini Magazine - - Tech -

I have just bought the gor­geous Mini that runs on 10-inch Minilite wheels. The engine is a 1275 from a Metro, but the fi­nal spec is un­known other than a Stage 3 head, K&N fil­ter, and a twin­box Man­i­flow ex­haust sys­tem. It’s fun for oc­ca­sional use, but it seems to have some very short legs and I’m hop­ing to use it for tour­ing around the coun­try a fair bit. On the mo­tor­way it’s pretty deafen­ing, so would fit­ting 12 inch wheels make any ap­pre­cia­ble dif­fer­ence, or must I go through the process of hav­ing of hav­ing a dif­fer­ent dif­fer­en­tial fit­ted? I`m not so both­ered about looks, I just want it to cruise bet­ter. Hamish

Al­though fit­ting 12-inch wheels and tyres seems like it should dra­mat­i­cally re­duce the engine speed, it doesn’t. The over­all rolling cir­cum­fer­ence is not a whole lot dif­fer­ent be­cause of the tyres’ con­struc­tion. The 1275 engine/gearbox units fit­ted to Met­ros al­most al­ways had a 3.44:1 fi­nal drive fit­ted. So that along with the 10-inch wheel set-up means around 16.17mph per 1,000rpm. So to make 70mph you would be us­ing around 4,325 rpm. By com­par­i­son on the same fi­nal drive, 12-inch wheels give 16.47mph per 1,000rpm, so not much change at all.

So, the only way to re­duce the rpm re­quired to cruise at mo­tor­way speeds you will need to change the fi­nal drive. Go­ing to a 3.105:1 would give you around 17.92mph per 1,000rpm. Still not a mas­sive change, but some. How­ever, it’s likely a great deal of noise may well be com­ing from the in­duc­tion noise where a re­place­ment cone or pan­cake fil­ter has been fit­ted in place of the stan­dard plas­tic air fil­ter cas­ing. So be­fore em­bark­ing on the ma­jor task of haul­ing the engine and ‘box to change the fi­nal drive, you should con­sider do­ing some­thing about that. Also, make sure ef­fec­tive sound proof­ing has been used, if fit­ted at all!

10-inch or 12-inch - de­ci­sion’s yours.

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