Hello

This is my first post on the forum so I apologise if it gets a little long winded.

I recently bought a spare pair of wheels for the DT. The rims and spokes were shot, but the price was worth it just for the hubs

I have paid for sm pro rims in black but they have told me they have stopped making the rear 18x1.85 and now only supply the 18x 2.15. I could cancel the order and buy else where but if the 2.15 is ok i will go with that one.(money and time is getting a little tight and the sm pro is a good price)

My bike is a 1979 reg with a round tube swinging arm and has a 4.00x18 cats paw tyre fitted to a 18x1.85 rim and is alright for clearance

Does anyone know if I would encounter any problems fitting the wider 2.15 rim but still with the 4.00 wide tyre

I have searched for preferred rim sizes for a 4.00 tyre but I tend to get bogged down

I can go one size either side of the tyre manufactures preferred rim size without altering the tyre profile too much for the type of use I require but its the clearance on the DT I’m unsure of

Hope some one can help

Cheers

Nobbie

In theory fitting a wider rim narrows the tyre when fitted, as it stretches the tyre over the rim it loses height and a little bulbousness.

However, is your supplier certain your rim will fit your hubs? As modern mx/enduro hubs are all spaced the same to

Make rim replacement easier. Older bikes tend to have their own offset/spacing.

This has an effect on how the.holes in the dimples are drilled on the rim. The angle differs from rim to rim.

For example compare the front hub of a dt 175 to another bike with a 21" rim. The front hub is concentric, having shorter spokes on the drum side. This affects spoke lengths, and therefore angles.

Use the wrong hub and the spokes will me fractionally bent at the nipples, and under tension this is not good.

The same goes for the rear. From memory A dt 175 has the same length spokes both sides, modern bikes have much smaller hubs, as no drum. Again meaning the angle is different.

If your new rim comes with no.holes you will have to get a wheel building company to drill them to your hubs.

I would be careful. There is not a lot of mud room as it is. I have been stopped more than once by mud jamming the wheel up.

Try and get the proper size would be my gambit. Esp for off road work.

thanks busyeddie

i should bloody well know all this

but trying to rush and get things done i was only looking at the relationship between tyre and rim and not spoke length and hole angles due to drums etc

and

yer right Cynic there isnt a deal of room down there to start with. Another little nugget i over looked in my haste

i will cancel my order. sit back have a brew and take my time.

one option may be central wheel builders. i believe they can drill to suit but at what price i dont know

thanks again chaps

or you coul fit the 3.5 tyre like it was when it was new

Yes I was trying to build a spare pair of wheels to fit the tires that came with the bike (still lots of tread)

I had fitted Mich AC10s to the original wheels for all the to cope with the treacherous snow .!!!!!

That lasted all of three days

Couldn’t be bothered to swap back, so decided on a spare set wheels

My option is ring central wheels for a quote for the STD 1.85 rim

Use the 4.00 tyre and then back to STD 3.50

Like an old geezer who knew his onions once said why bother over tyring a bike just run as the manufacturer designed it

Thanks for the help

did the ac10 fit ok?

Yes it did

I thought I may have had to move the wheel further down the swinging arm (I’m on a new STD length chain so the wheel is as close into the arm as it will ever be) but I didn’t have to

There was I slight rubbing I could hear on the chain guard when I spun the wheel. It was too dark at the time to see where. So I removed it

Don’t like running without the guard, but days are getting lighter now so I will pop it back on and see if a little trimming of the guard will sort it

If its that close stay off the dirt.

I tried some mud tyres on mine that just cleared and i just kept getting stopped by the mud jamming stuff up.

I ended up with a plain block pattern bridgestone road tyre and a full knobbly up front. That was real good in the dirt, so long as you kept it spinning.

Cynic is right

it would be way to close for mud plugging even if the wheel was at the end of the swinging arm, and there is very little side clearance

As said eariler I fitted the AC10s to combat all the snow that was forcast

and living off the beaten track in " the last of the summer wine county" they served me well. All be it for a short period

Riding down the hills I passed three men with flat caps in a bath on wheels several times

As fas as the tyre to the rim fit a 2.50 is optimum, the next size down is OK and the next up. So from that point of view the rim and tyre combination is safe. The Japanese used very undersized rims for the tyre size - why I don't know.

You find that a tyre stretched over the correct sized rims is not as wide as you'd think. I put a 3.0 inch rim on an SR500 with a 130/80 tyre, thinking that was going to be tight on clearance. What I found was as the tyre fitted the rim correctly there was considerably more clearance then I calculated.

I'm not saying this will follow on all bikes and you will need much more clearance for mud then on a road bike!