Hi there,

I've just bought a new rear wheel for my road bike, it has a 7 cassette on it and the previous wheel was a 6 freewheel it doesn't run smoothly feels like it's skipping even with very minor adjustments to it's placement, Do I need a new rear mech because of the difference from freewheel to cassette?

Thanks

As time passes, chains and gear clusters (either freewheel or cassette) mate. Once this happens neither will gracefully accept a replacement of the other. You need to buy a new chain. Your derailleur is probably fine, but the limit screws should be adjusted for the new cassette.

It ran perfectly fine with my old wheel and 6-speed freewheel, this has only happened since the new wheel with the 7 cassette. when I turn the bike over and pedal it makes a loud rev type of noise

Again, unless you fitted a new chain with the new cassette, you are going to have skipping and noise problems. BTW, are your shifters either friction or 7-speed compatible? If they are indexed for 6-speed, they won't work properly.

Ahh so is it because the chain is too wide for the cassette? the shifters are on the frame and don't click into place they are able to be moved freely. will it damage my bike if I run it like this btw? Thanks

Start by separating the wheat from the chaff. Does it grind only pedaling or only when coasting, or both?

Both points to hub bearings.
while pedaling points to chain/sprocket noise
while coasting points to freewheel mechanism noise.

Once you've localized the problem, then you can try to isolate the exact cause.

Only when I pedal, it's a brand-new wheel and cassette but a very old chain. when I flip the bike over and pedal I can feel like a vibrating sensation in the pedals. chains probably 7 years old should I just get a new chain? would that sort the problem out? thanks

OK so we know it's a chain/sprocket issue. Based on the description and the age of the chain, I'd guess the chain is stretched (worn out). You can confirm this with a 12" ruler. Put some tension in the lower loop by pulling the RDs lower pulley back slightly. Measure 12" (24 links) of chain. Since the chain is 1/2" pitch all pins should line up at 1/2" marks, and 12" should measure exactly 12" pin to pin on centers.

However wear at the pins allow the links to pull apart a bit, and with the accumulated error will have the last pin visibly beyond the 12" mark by a bit. If it's near 1/16" off, replace the chain before it accelerates wear on your new cassette.

I measured it but in cm only have a 6inch ruler, I got 8 pins in 9cm including the first one it was very very slightly more than 9cm from the center of the first and last maybe 0.5mm more

Just checked with a ruler with inches on, the final pin is 3mm more than 6 inches so my guess is from a 12" ruler it's about 1/4-1/5th of an inch off

New sprockets call for new chain.

Thanks for all th help guys going to get a new Chain! I'll let you know if it's fixed the problem

You have 6" ruler, and a 1/2" pitch chain, why are you measuring anything in cm? Nothing wrong with the metric system, but here's an example where using inches makes infinitely more sense. If you can't find an inch ruler, calculate how many cm in 6" (152.4mm) and compare the stretch over 12 links to that, with the pass/fail line at 0.8mm, or 153mm total.

BTW even if it's borderline, it's better to replace the chain anytime you replace a cassette because a worn chain will rapidly wear a cassette to match it's condition.

I found an inch ruler in the end in 6 inches the 12th pin was 3mm out so difinitely need a new chain! would you say it's safe to ride 10miles with this chain to go get a new one? Thanks

Yes, it's safe. Even at an accelerated rate wear is a slow process. 10 miles is nothing in the scheme of things.

Okay thanks! Will get a new chain tomorrow!

10 miles, sure, but not a meter more.